esm: phase two of new esm implementation

This PR updates the current `--experimental-modules` implementation
based on the work of the modules team  and reflects Phase 2 of our
new modules plan.

The largest differences from the current implementation include

* `packge.type` which can be either `module` or `commonjs`
  - `type: "commonjs"`:
    - `.js` is parsed as commonjs
    - default for entry point without an extension is commonjs
  - `type: "module"`:
    - `.js` is parsed as esm
    - does not support loading JSON or Native Module by default
    - default for entry point without an extension is esm
* `--entry-type=[mode]`
  - allows you set the type on entry point.
* A new file extension `.cjs`.
  - this is specifically to support importing commonjs in the
    `module` mode.
  - this is only in the esm loader, the commonjs loader remains
    untouched, but the extension will work in the old loader if you use
    the full file path.
* `--es-module-specifier-resolution=[type]`
  - options are `explicit` (default) and `node`
  - by default our loader will not allow for optional extensions in
    the import, the path for a module must include the extension if
    there is one
  - by default our loader will not allow for importing directories that
    have an index file
  - developers can use `--es-module-specifier-resolution=node` to
    enable the commonjs specifier resolution algorithm
  - This is not a “feature” but rather an implementation for
    experimentation. It is expected to change before the flag is
    removed
* `--experimental-json-loader`
  - the only way to import json when `"type": "module"`
  - when enable all `import 'thing.json'` will go through the
    experimental loader independent of mode
  - based on https://github.com/whatwg/html/issues/4315
* You can use `package.main` to set an entry point for a module
  - the file extensions used in main will be resolved based on the
    `type` of the module

Refs: https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md
Refs: https://github.com/GeoffreyBooth/node-import-file-specifier-resolution-proposal
Refs: https://github.com/nodejs/modules/pull/180
Refs: https://github.com/nodejs/ecmascript-modules/pull/6
Refs: https://github.com/nodejs/ecmascript-modules/pull/12
Refs: https://github.com/nodejs/ecmascript-modules/pull/28
Refs: https://github.com/nodejs/modules/issues/255
Refs: https://github.com/whatwg/html/issues/4315
Refs: https://github.com/w3c/webcomponents/issues/770
Co-authored-by: Myles Borins <MylesBorins@google.com>
Co-authored-by: John-David Dalton <john.david.dalton@gmail.com>
Co-authored-by: Evan Plaice <evanplaice@gmail.com>
Co-authored-by: Geoffrey Booth <webmaster@geoffreybooth.com>
Co-authored-by: Michaël Zasso <targos@protonmail.com>

PR-URL: https://github.com/nodejs/node/pull/26745
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Ben Coe <bencoe@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

124 files changed, 1822 insertions, 482 deletions

diff --git a/.eslintrc.js b/.eslintrc.js
index 54595a8b74..d3a6c73241 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -38,6 +38,8 @@ module.exports = {
     {
       files: [
         'doc/api/esm.md',
+        'test/es-module/test-esm-type-flag.js',
+        'test/es-module/test-esm-type-flag-alias.js',
         '*.mjs',
         'test/es-module/test-esm-example-loader.js',
       ],
diff --git a/doc/api/cli.md b/doc/api/cli.md
index 4c5c8fb618..ad7b65e90a 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -131,9 +131,43 @@ conjunction with native stack and other runtime environment data.
 added: v6.0.0
 -->
 
+### `--entry-type=type`
+<!-- YAML
+added: REPLACEME
+-->
+
+Used with `--experimental-modules`, this configures Node.js to interpret the
+initial entry point as CommonJS or as an ES module.
+
+Valid values are `"commonjs"` and `"module"`. The default is to infer from
+the file extension and the `"type"` field in the nearest parent `package.json`.
+
+Works for executing a file as well as `--eval`, `--print`, `STDIN`.
+
 Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with
 `./configure --openssl-fips`.)
 
+### `--es-module-specifier-resolution=mode`
+<!-- YAML
+added: REPLACEME
+-->
+
+To be used in conjunction with `--experimental-modules`. Sets the resolution
+algorithm for resolving specifiers. Valid options are `explicit` and `node`.
+
+The default is `explicit`, which requires providing the full path to a
+module. The `node` mode will enable support for optional file extensions and
+the ability to import a directory that has an index file.
+
+Please see [customizing esm specifier resolution][] for example usage.
+
+### `--experimental-json-modules`
+<!-- YAML
+added: REPLACEME
+-->
+
+Enable experimental JSON support for the ES Module loader.
+
 ### `--experimental-modules`
 <!-- YAML
 added: v8.5.0
@@ -927,9 +961,10 @@ greater than `4` (its current default value). For more information, see the
 [REPL]: repl.html
 [ScriptCoverage]: https://chromedevtools.github.io/devtools-protocol/tot/Profiler#type-ScriptCoverage
 [V8 JavaScript code coverage]: https://v8project.blogspot.com/2017/12/javascript-code-coverage.html
+[customizing esm specifier resolution]: esm.html#esm_customizing_esm_specifier_resolution_algorithm
 [debugger]: debugger.html
 [debugging security implications]: https://nodejs.org/en/docs/guides/debugging-getting-started/#security-implications
 [emit_warning]: process.html#process_process_emitwarning_warning_type_code_ctor
-[experimental ECMAScript Module]: esm.html#esm_loader_hooks
+[experimental ECMAScript Module]: esm.html#esm_resolve_hook
 [libuv threadpool documentation]: http://docs.libuv.org/en/latest/threadpool.html
 [remote code execution]: https://www.owasp.org/index.php/Code_Injection
diff --git a/doc/api/errors.md b/doc/api/errors.md
index 7e32ba1cfc..0161853774 100644
--- a/doc/api/errors.md
+++ b/doc/api/errors.md
@@ -844,6 +844,18 @@ provided.
 Encoding provided to `TextDecoder()` API was not one of the
 [WHATWG Supported Encodings][].
 
+<a id="ERR_ENTRY_TYPE_MISMATCH"></a>
+#### ERR_ENTRY_TYPE_MISMATCH
+
+> Stability: 1 - Experimental
+
+The `--entry-type=commonjs` flag was used to attempt to execute an `.mjs` file
+or a `.js` file where the nearest parent `package.json` contains
+`"type": "module"`; or
+the `--entry-type=module` flag was used to attempt to execute a `.cjs` file or
+a `.js` file where the nearest parent `package.json` either lacks a `"type"`
+field or contains `"type": "commonjs"`.
+
 <a id="ERR_FALSY_VALUE_REJECTION"></a>
 ### ERR_FALSY_VALUE_REJECTION
 
@@ -1267,6 +1279,11 @@ An invalid or unexpected value was passed in an options object.
 
 An invalid or unknown file encoding was passed.
 
+<a id="ERR_INVALID_PACKAGE_CONFIG"></a>
+### ERR_INVALID_PACKAGE_CONFIG
+
+An invalid `package.json` file was found which failed parsing.
+
 <a id="ERR_INVALID_PERFORMANCE_MARK"></a>
 ### ERR_INVALID_PERFORMANCE_MARK
 
@@ -1440,7 +1457,7 @@ strict compliance with the API specification (which in some cases may accept
 
 > Stability: 1 - Experimental
 
-An [ES6 module][] loader hook specified `format: 'dynamic'` but did not provide
+An [ES Module][] loader hook specified `format: 'dynamic'` but did not provide
 a `dynamicInstantiate` hook.
 
 <a id="ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST"></a>
@@ -1449,13 +1466,6 @@ a `dynamicInstantiate` hook.
 A `MessagePort` was found in the object passed to a `postMessage()` call,
 but not provided in the `transferList` for that call.
 
-<a id="ERR_MISSING_MODULE"></a>
-### ERR_MISSING_MODULE
-
-> Stability: 1 - Experimental
-
-An [ES6 module][] could not be resolved.
-
 <a id="ERR_MISSING_PLATFORM_FOR_WORKER"></a>
 ### ERR_MISSING_PLATFORM_FOR_WORKER
 
@@ -1463,12 +1473,12 @@ The V8 platform used by this instance of Node.js does not support creating
 Workers. This is caused by lack of embedder support for Workers. In particular,
 this error will not occur with standard builds of Node.js.
 
-<a id="ERR_MODULE_RESOLUTION_LEGACY"></a>
-### ERR_MODULE_RESOLUTION_LEGACY
+<a id="ERR_MODULE_NOT_FOUND"></a>
+### ERR_MODULE_NOT_FOUND
 
 > Stability: 1 - Experimental
 
-A failure occurred resolving imports in an [ES6 module][].
+An [ES Module][] could not be resolved.
 
 <a id="ERR_MULTIPLE_CALLBACK"></a>
 ### ERR_MULTIPLE_CALLBACK
@@ -1555,7 +1565,7 @@ A given value is out of the accepted range.
 
 > Stability: 1 - Experimental
 
-An attempt was made to `require()` an [ES6 module][].
+An attempt was made to `require()` an [ES Module][].
 
 <a id="ERR_SCRIPT_EXECUTION_INTERRUPTED"></a>
 ### ERR_SCRIPT_EXECUTION_INTERRUPTED
@@ -2220,10 +2230,17 @@ A non-specific HTTP/2 error has occurred.
 Used in the `repl` in case the old history file is used and an error occurred
 while trying to read and parse it.
 
+<a id="ERR_INVALID_REPL_TYPE"></a>
+#### ERR_INVALID_REPL_TYPE
+
+> Stability: 1 - Experimental
+
+The `--entry-type=...` flag is not compatible with the Node.js REPL.
+
 <a id="ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK"></a>
 #### ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK
 
-Used when an [ES6 module][] loader hook specifies `format: 'dynamic'` but does
+Used when an [ES Module][] loader hook specifies `format: 'dynamic'` but does
 not provide a `dynamicInstantiate` hook.
 
 <a id="ERR_STREAM_HAS_STRINGDECODER"></a>
@@ -2250,7 +2267,6 @@ size.
 This `Error` is thrown when a read is attempted on a TTY `WriteStream`,
 such as `process.stdout.on('data')`.
 
-
 [`'uncaughtException'`]: process.html#process_event_uncaughtexception
 [`--force-fips`]: cli.html#cli_force_fips
 [`Class: assert.AssertionError`]: assert.html#assert_class_assert_assertionerror
@@ -2293,7 +2309,7 @@ such as `process.stdout.on('data')`.
 [`subprocess.kill()`]: child_process.html#child_process_subprocess_kill_signal
 [`subprocess.send()`]: child_process.html#child_process_subprocess_send_message_sendhandle_options_callback
 [`zlib`]: zlib.html
-[ES6 module]: esm.html
+[ES Module]: esm.html
 [ICU]: intl.html#intl_internationalization_support
 [Node.js Error Codes]: #nodejs-error-codes
 [V8's stack trace API]: https://github.com/v8/v8/wiki/Stack-Trace-API
diff --git a/doc/api/esm.md b/doc/api/esm.md
index e81a69c6ed..ce616e1f42 100644
--- a/doc/api/esm.md
+++ b/doc/api/esm.md
@@ -5,39 +5,233 @@
 
 > Stability: 1 - Experimental
 
+## Introduction
+
 <!--name=esm-->
 
+ECMAScript modules are [the official standard format][] to package JavaScript
+code for reuse. Modules are defined using a variety of [`import`][] and
+[`export`][] statements.
+
+Node.js fully supports ECMAScript modules as they are currently specified and
+provides limited interoperability between them and the existing module format,
+[CommonJS][].
+
 Node.js contains support for ES Modules based upon the
-[Node.js EP for ES Modules][].
+[Node.js EP for ES Modules][] and the [ECMAScript-modules implementation][].
 
-Not all features of the EP are complete and will be landing as both VM support
-and implementation is ready. Error messages are still being polished.
+Expect major changes in the implementation including interoperability support,
+specifier resolution, and default behavior.
 
 ## Enabling
 
 <!-- type=misc -->
 
-The `--experimental-modules` flag can be used to enable features for loading
-ESM modules.
+The `--experimental-modules` flag can be used to enable support for
+ECMAScript modules (ES modules).
+
+## Running Node.js with an ECMAScript Module
 
-Once this has been set, files ending with `.mjs` will be able to be loaded
-as ES Modules.
+There are a few ways to start Node.js with an ES module as its input.
+
+### Initial entry point with an <code>.mjs</code> extension
+
+A file ending with `.mjs` passed to Node.js as an initial entry point will be
+loaded as an ES module.
 
 ```sh
 node --experimental-modules my-app.mjs
 ```
 
-## Features
+### <code>--entry-type=module</code> flag
 
-<!-- type=misc -->
+Files ending with `.js` or `.mjs`, or lacking any extension,
+will be loaded as ES modules when the `--entry-type=module` flag is set.
+
+```sh
+node --experimental-modules --entry-type=module my-app.js
+```
+
+For completeness there is also `--entry-type=commonjs`, for explicitly running
+a `.js` file as CommonJS. This is the default behavior if `--entry-type` is
+unspecified.
+
+The `--entry-type=module` flag can also be used to configure Node.js to treat
+as an ES module input sent in via `--eval` or `--print` (or `-e` or `-p`) or
+piped to Node.js via `STDIN`.
+
+```sh
+node --experimental-modules --entry-type=module --eval \
+  "import { sep } from 'path'; console.log(sep);"
+
+echo "import { sep } from 'path'; console.log(sep);" | \
+  node --experimental-modules --entry-type=module
+```
+
+### <code>package.json</code> <code>"type"</code> field
+
+Files ending with `.js` or `.mjs`, or lacking any extension,
+will be loaded as ES modules when the nearest parent `package.json` file
+contains a top-level field `"type"` with a value of `"module"`.
+
+The nearest parent `package.json` is defined as the first `package.json` found
+when searching in the current folder, that folder’s parent, and so on up
+until the root of the volume is reached.
+
+<!-- eslint-skip -->
+```js
+// package.json
+{
+  "type": "module"
+}
+```
+
+```sh
+# In same folder as above package.json
+node --experimental-modules my-app.js # Runs as ES module
+```
+
+If the nearest parent `package.json` lacks a `"type"` field, or contains
+`"type": "commonjs"`, extensionless and `.js` files are treated as CommonJS.
+If the volume root is reached and no `package.json` is found,
+Node.js defers to the default, a `package.json` with no `"type"`
+field.
+
+## Package Scope and File Extensions
+
+A folder containing a `package.json` file, and all subfolders below that
+folder down until the next folder containing another `package.json`, is
+considered a _package scope_. The `"type"` field defines how `.js` and
+extensionless files should be treated within a particular `package.json` file’s
+package scope. Every package in a project’s `node_modules` folder contains its
+own `package.json` file, so each project’s dependencies have their own package
+scopes. A `package.json` lacking a `"type"` field is treated as if it contained
+`"type": "commonjs"`.
+
+The package scope applies not only to initial entry points (`node
+--experimental-modules my-app.js`) but also to files referenced by `import`
+statements and `import()` expressions.
+
+```js
+// my-app.js, in an ES module package scope because there is a package.json
+// file in the same folder with "type": "module".
+
+import './startup/init.js';
+// Loaded as ES module since ./startup contains no package.json file,
+// and therefore inherits the ES module package scope from one level up.
+
+import 'commonjs-package';
+// Loaded as CommonJS since ./node_modules/commonjs-package/package.json
+// lacks a "type" field or contains "type": "commonjs".
+
+import './node_modules/commonjs-package/index.js';
+// Loaded as CommonJS since ./node_modules/commonjs-package/package.json
+// lacks a "type" field or contains "type": "commonjs".
+```
+
+Files ending with `.mjs` are always loaded as ES modules regardless of package
+scope.
+
+Files ending with `.cjs` are always loaded as CommonJS regardless of package
+scope.
+
+```js
+import './legacy-file.cjs';
+// Loaded as CommonJS since .cjs is always loaded as CommonJS.
+
+import 'commonjs-package/src/index.mjs';
+// Loaded as ES module since .mjs is always loaded as ES module.
+```
+
+The `.mjs` and `.cjs` extensions may be used to mix types within the same
+package scope:
+
+- Within a `"type": "module"` package scope, Node.js can be instructed to
+  interpret a particular file as CommonJS by naming it with a `.cjs` extension
+  (since both `.js` and `.mjs` files are treated as ES modules within a
+  `"module"` package scope).
+
+- Within a `"type": "commonjs"` package scope, Node.js can be instructed to
+  interpret a particular file as an ES module by naming it with an `.mjs`
+  extension (since both `.js` and `.cjs` files are treated as CommonJS within a
+  `"commonjs"` package scope).
+
+## Package Entry Points
+
+The `package.json` `"main"` field defines the entry point for a package,
+whether the package is included into CommonJS via `require` or into an ES
+module via `import`.
+
+<!-- eslint-skip -->
+```js
+// ./node_modules/es-module-package/package.json
+{
+  "type": "module",
+  "main": "./src/index.js"
+}
+```
+```js
+// ./my-app.mjs
+
+import { something } from 'es-module-package';
+// Loads from ./node_modules/es-module-package/src/index.js
+```
+
+An attempt to `require` the above `es-module-package` would attempt to load
+`./node_modules/es-module-package/src/index.js` as CommonJS, which would throw
+an error as Node.js would not be able to parse the `export` statement in
+CommonJS.
+
+As with `import` statements, for ES module usage the value of `"main"` must be
+a full path including extension: `"./index.mjs"`, not `"./index"`.
+
+If the `package.json` `"type"` field is omitted, a `.js` file in `"main"` will
+be interpreted as CommonJS.
+
+> Currently a package can define _either_ a CommonJS entry point **or** an ES
+> module entry point; there is no way to specify separate entry points for
+> CommonJS and ES module usage. This means that a package entry point can be
+> included via `require` or via `import` but not both.
+>
+> Such a limitation makes it difficult for packages to support both new versions
+> of Node.js that understand ES modules and older versions of Node.js that
+> understand only CommonJS. There is work ongoing to remove this limitation, and
+> it will very likely entail changes to the behavior of `"main"` as defined
+> here.
+
+## <code>import</code> Specifiers
+
+### Terminology
+
+The _specifier_ of an `import` statement is the string after the `from` keyword,
+e.g. `'path'` in `import { sep } from 'path'`. Specifiers are also used in
+`export from` statements, and as the argument to an `import()` expression.
+
+There are four types of specifiers:
+
+- _Bare specifiers_ like `'some-package'`. They refer to an entry point of a
+  package by the package name.
+
+- _Deep import specifiers_ like `'some-package/lib/shuffle.mjs'`. They refer to
+  a path within a package prefixed by the package name.
+
+- _Relative specifiers_ like `'./startup.js'` or `'../config.mjs'`. They refer
+  to a path relative to the location of the importing file.
+
+- _Absolute specifiers_ like `'file:///opt/nodejs/config.js'`. They refer
+  directly and explicitly to a full path.
+
+Bare specifiers, and the bare specifier portion of deep import specifiers, are
+strings; but everything else in a specifier is a URL.
 
-### Supported
+Only `file://` URLs are supported. A specifier like
+`'https://example.com/app.js'` may be supported by browsers but it is not
+supported in Node.js.
 
-Only the CLI argument for the main entry point to the program can be an entry
-point into an ESM graph. Dynamic import can also be used to create entry points
-into ESM graphs at runtime.
+Specifiers may not begin with `/` or `//`. These are reserved for potential
+future use. The root of the current volume may be referenced via `file:///`.
 
-#### import.meta
+## import.meta
 
 * {Object}
 
@@ -46,63 +240,128 @@ property:
 
 * `url` {string} The absolute `file:` URL of the module.
 
-### Unsupported
+## Differences Between ES Modules and CommonJS
 
-| Feature | Reason |
-| --- | --- |
-| `require('./foo.mjs')` | ES Modules have differing resolution and timing, use dynamic import |
+### Mandatory file extensions
+
+A file extension must be provided when using the `import` keyword. Directory
+indexes (e.g. `'./startup/index.js'`) must also be fully specified.
 
-## Notable differences between `import` and `require`
+This behavior matches how `import` behaves in browser environments, assuming a
+typically configured server.
 
-### No NODE_PATH
+### No <code>NODE_PATH</code>
 
 `NODE_PATH` is not part of resolving `import` specifiers. Please use symlinks
 if this behavior is desired.
 
-### No `require.extensions`
+### No <code>require</code>, <code>exports</code>, <code>module.exports</code>, <code>\_\_filename</code>, <code>\_\_dirname</code>
+
+These CommonJS variables are not available in ES modules.
+
+`require` can be imported into an ES module using
+[`module.createRequireFromPath()`][].
+
+An equivalent for `__filename` and `__dirname` is [`import.meta.url`][].
+
+### No <code>require.extensions</code>
 
 `require.extensions` is not used by `import`. The expectation is that loader
 hooks can provide this workflow in the future.
 
-### No `require.cache`
+### No <code>require.cache</code>
 
 `require.cache` is not used by `import`. It has a separate cache.
 
-### URL based paths
+### URL-based paths
 
-ESM are resolved and cached based upon [URL](https://url.spec.whatwg.org/)
-semantics. This means that files containing special characters such as `#` and
-`?` need to be escaped.
+ES modules are resolved and cached based upon
+[URL](https://url.spec.whatwg.org/) semantics. This means that files containing
+special characters such as `#` and `?` need to be escaped.
 
 Modules will be loaded multiple times if the `import` specifier used to resolve
 them have a different query or fragment.
 
 ```js
-import './foo?query=1'; // loads ./foo with query of "?query=1"
-import './foo?query=2'; // loads ./foo with query of "?query=2"
+import './foo.mjs?query=1'; // loads ./foo.mjs with query of "?query=1"
+import './foo.mjs?query=2'; // loads ./foo.mjs with query of "?query=2"
 ```
 
 For now, only modules using the `file:` protocol can be loaded.
 
-## Interop with existing modules
+## Interoperability with CommonJS
+
+### <code>require</code>
 
-All CommonJS, JSON, and C++ modules can be used with `import`.
+`require` always treats the files it references as CommonJS. This applies
+whether `require` is used the traditional way within a CommonJS environment, or
+in an ES module environment using [`module.createRequireFromPath()`][].
 
-Modules loaded this way will only be loaded once, even if their query
-or fragment string differs between `import` statements.
+To include an ES module into CommonJS, use [`import()`][].
 
-When loaded via `import` these modules will provide a single `default` export
-representing the value of `module.exports` at the time they finished evaluating.
+### <code>import</code> statements
+
+An `import` statement can reference either ES module or CommonJS JavaScript.
+Other file types such as JSON and Native modules are not supported. For those,
+use [`module.createRequireFromPath()`][].
+
+`import` statements are permitted only in ES modules. For similar functionality
+in CommonJS, see [`import()`][].
+
+The _specifier_ of an `import` statement (the string after the `from` keyword)
+can either be an URL-style relative path like `'./file.mjs'` or a package name
+like `'fs'`.
+
+Like in CommonJS, files within packages can be accessed by appending a path to
+the package name.
 
 ```js
-// foo.js
-module.exports = { one: 1 };
+import { sin, cos } from 'geometry/trigonometry-functions.mjs';
+```
+
+> Currently only the “default export” is supported for CommonJS files or
+> packages:
+>
+> <!-- eslint-disable no-duplicate-imports -->
+> ```js
+> import packageMain from 'commonjs-package'; // Works
+>
+> import { method } from 'commonjs-package'; // Errors
+> ```
+>
+> There are ongoing efforts to make the latter code possible.
 
-// bar.mjs
-import foo from './foo.js';
-foo.one === 1; // true
+### <code>import()</code> expressions
+
+Dynamic `import()` is supported in both CommonJS and ES modules. It can be used
+to include ES module files from CommonJS code.
+
+```js
+(async () => {
+  await import('./my-app.mjs');
+})();
 ```
 
+## CommonJS, JSON, and Native Modules
+
+CommonJS, JSON, and Native modules can be used with [`module.createRequireFromPath()`][].
+
+```js
+// cjs.js
+module.exports = 'cjs';
+
+// esm.mjs
+import { createRequireFromPath as createRequire } from 'module';
+import { fileURLToPath as fromURL } from 'url';
+
+const require = createRequire(fromURL(import.meta.url));
+
+const cjs = require('./cjs');
+cjs === 'cjs'; // true
+```
+
+## Builtin modules
+
 Builtin modules will provide named exports of their public API, as well as a
 default export which can be used for, among other things, modifying the named
 exports. Named exports of builtin modules are updated when the corresponding
@@ -132,7 +391,41 @@ fs.readFileSync = () => Buffer.from('Hello, ESM');
 fs.readFileSync === readFileSync;
 ```
 
-## Loader hooks
+## Experimental JSON Modules
+
+**Note: This API is still being designed and is subject to change.**
+
+Currently importing JSON modules are only supported in the `commonjs` mode
+and are loaded using the CJS loader. [WHATWG JSON modules][] are currently
+being standardized, and are experimentally supported by including the
+additional flag `--experimental-json-modules` when running Node.js.
+
+When the `--experimental-json-modules` flag is included both the
+`commonjs` and `module` mode will use the new experimental JSON
+loader. The imported JSON only exposes a `default`, there is no
+support for named exports. A cache entry is created in the CommonJS
+cache, to avoid duplication. The same object will be returned in
+CommonJS if the JSON module has already been imported from the
+same path.
+
+Assuming an `index.js` with
+
+<!-- eslint-skip -->
+```js
+import packageConfig from './package.json';
+```
+
+The `--experimental-json-modules` flag is needed for the module
+to work.
+
+```bash
+node --experimental-modules --entry-type=module index.js # fails
+node --experimental-modules --entry-type=module --experimental-json-modules index.js # works
+```
+
+## Experimental Loader hooks
+
+**Note: This API is currently being redesigned and will still change.**
 
 <!-- type=misc -->
 
@@ -173,11 +466,10 @@ module. This can be one of the following:
 
 | `format` | Description |
 | --- | --- |
-| `'esm'` | Load a standard JavaScript module |
-| `'cjs'` | Load a node-style CommonJS module |
-| `'builtin'` | Load a node builtin CommonJS module |
+| `'module'` | Load a standard JavaScript module |
+| `'commonjs'` | Load a Node.js CommonJS module |
+| `'builtin'` | Load a Node.js builtin module |
 | `'json'` | Load a JSON file |
-| `'addon'` | Load a [C++ Addon][addons] |
 | `'dynamic'` | Use a [dynamic instantiate hook][] |
 
 For example, a dummy loader to load JavaScript restricted to browser resolution
@@ -253,6 +545,184 @@ With the list of module exports provided upfront, the `execute` function will
 then be called at the exact point of module evaluation order for that module
 in the import tree.
 
+## Resolution Algorithm
+
+### Features
+
+The resolver has the following properties:
+
+* FileURL-based resolution as is used by ES modules
+* Support for builtin module loading
+* Relative and absolute URL resolution
+* No default extensions
+* No folder mains
+* Bare specifier package resolution lookup through node_modules
+
+### Resolver Algorithm
+
+The algorithm to load an ES module specifier is given through the
+**ESM_RESOLVE** method below. It returns the resolved URL for a
+module specifier relative to a parentURL, in addition to the unique module
+format for that resolved URL given by the **ESM_FORMAT** routine.
+
+The _"module"_ format is returned for an ECMAScript Module, while the
+_"commonjs"_ format is used to indicate loading through the legacy
+CommonJS loader. Additional formats such as _"wasm"_ or _"addon"_ can be
+extended in future updates.
+
+In the following algorithms, all subroutine errors are propagated as errors
+of these top-level routines.
+
+_isMain_ is **true** when resolving the Node.js application entry point.
+
+When using the `--entry-type` flag, it overrides the ESM_FORMAT result while
+providing errors in the case of explicit conflicts.
+
+<details>
+<summary>Resolver algorithm specification</summary>
+
+**ESM_RESOLVE(_specifier_, _parentURL_, _isMain_)**
+> 1. Let _resolvedURL_ be **undefined**.
+> 1. If _specifier_ is a valid URL, then
+>    1. Set _resolvedURL_ to the result of parsing and reserializing
+>       _specifier_ as a URL.
+> 1. Otherwise, if _specifier_ starts with _"/"_, then
+>    1. Throw an _Invalid Specifier_ error.
+> 1. Otherwise, if _specifier_ starts with _"./"_ or _"../"_, then
+>    1. Set _resolvedURL_ to the URL resolution of _specifier_ relative to
+>       _parentURL_.
+> 1. Otherwise,
+>    1. Note: _specifier_ is now a bare specifier.
+>    1. Set _resolvedURL_ the result of
+>       **PACKAGE_RESOLVE**(_specifier_, _parentURL_).
+> 1. If the file at _resolvedURL_ does not exist, then
+>    1. Throw a _Module Not Found_ error.
+> 1. Set _resolvedURL_ to the real path of _resolvedURL_.
+> 1. Let _format_ be the result of **ESM_FORMAT**(_resolvedURL_, _isMain_).
+> 1. Load _resolvedURL_ as module format, _format_.
+
+PACKAGE_RESOLVE(_packageSpecifier_, _parentURL_)
+> 1. Let _packageName_ be *undefined*.
+> 1. Let _packageSubpath_ be *undefined*.
+> 1. If _packageSpecifier_ is an empty string, then
+>    1. Throw an _Invalid Specifier_ error.
+> 1. If _packageSpecifier_ does not start with _"@"_, then
+>    1. Set _packageName_ to the substring of _packageSpecifier_ until the
+>       first _"/"_ separator or the end of the string.
+> 1. Otherwise,
+>    1. If _packageSpecifier_ does not contain a _"/"_ separator, then
+>       1. Throw an _Invalid Specifier_ error.
+>    1. Set _packageName_ to the substring of _packageSpecifier_
+>       until the second _"/"_ separator or the end of the string.
+> 1. Let _packageSubpath_ be the substring of _packageSpecifier_ from the
+>    position at the length of _packageName_ plus one, if any.
+> 1. Assert: _packageName_ is a valid package name or scoped package name.
+> 1. Assert: _packageSubpath_ is either empty, or a path without a leading
+>    separator.
+> 1. If _packageSubpath_ contains any _"."_ or _".."_ segments or percent
+>    encoded strings for _"/"_ or _"\\"_ then,
+>    1. Throw an _Invalid Specifier_ error.
+> 1. If _packageSubpath_ is empty and _packageName_ is a Node.js builtin
+>    module, then
+>    1. Return the string _"node:"_ concatenated with _packageSpecifier_.
+> 1. While _parentURL_ is not the file system root,
+>    1. Let _packageURL_ be the URL resolution of "node_modules/"
+>       concatenated with _packageSpecifier_, relative to _parentURL_.
+>    1. Set _parentURL_ to the parent folder URL of _parentURL_.
+>    1. If the folder at _packageURL_ does not exist, then
+>       1. Set _parentURL_ to the parent URL path of _parentURL_.
+>       1. Continue the next loop iteration.
+>    1. Let _pjson_ be the result of **READ_PACKAGE_JSON**(_packageURL_).
+>    1. If _packageSubpath_ is empty, then
+>       1. Return the result of **PACKAGE_MAIN_RESOLVE**(_packageURL_,
+>          _pjson_).
+>    1. Otherwise,
+>       1. Return the URL resolution of _packageSubpath_ in _packageURL_.
+> 1. Throw a _Module Not Found_ error.
+
+PACKAGE_MAIN_RESOLVE(_packageURL_, _pjson_)
+> 1. If _pjson_ is **null**, then
+>    1. Throw a _Module Not Found_ error.
+> 1. If _pjson.main_ is a String, then
+>    1. Let _resolvedMain_ be the concatenation of _packageURL_, "/", and
+>       _pjson.main_.
+>    1. If the file at _resolvedMain_ exists, then
+>       1. Return _resolvedMain_.
+> 1. If _pjson.type_ is equal to _"module"_, then
+>    1. Throw a _Module Not Found_ error.
+> 1. Let _legacyMainURL_ be the result applying the legacy
+>    **LOAD_AS_DIRECTORY** CommonJS resolver to _packageURL_, throwing a
+>    _Module Not Found_ error for no resolution.
+> 1. If _legacyMainURL_ does not end in _".js"_ then,
+>    1. Throw an _Unsupported File Extension_ error.
+> 1. Return _legacyMainURL_.
+
+**ESM_FORMAT(_url_, _isMain_)**
+> 1. Assert: _url_ corresponds to an existing file.
+> 1. Let _pjson_ be the result of **READ_PACKAGE_SCOPE**(_url_).
+> 1. If _url_ ends in _".mjs"_, then
+>    1. Return _"module"_.
+> 1. If _url_ ends in _".cjs"_, then
+>    1. Return _"commonjs"_.
+> 1. If _pjson?.type_ exists and is _"module"_, then
+>    1. If _isMain_ is **true** or _url_ ends in _".js"_, then
+>       1. Return _"module"_.
+>    1. Throw an _Unsupported File Extension_ error.
+> 1. Otherwise,
+>    1. If _isMain_ is **true** or _url_ ends in _".js"_, _".json"_ or
+>       _".node"_, then
+>       1. Return _"commonjs"_.
+>    1. Throw an _Unsupported File Extension_ error.
+
+READ_PACKAGE_SCOPE(_url_)
+> 1. Let _scopeURL_ be _url_.
+> 1. While _scopeURL_ is not the file system root,
+>    1. Let _pjson_ be the result of **READ_PACKAGE_JSON**(_scopeURL_).
+>    1. If _pjson_ is not **null**, then
+>       1. Return _pjson_.
+>    1. Set _scopeURL_ to the parent URL of _scopeURL_.
+> 1. Return **null**.
+
+READ_PACKAGE_JSON(_packageURL_)
+> 1. Let _pjsonURL_ be the resolution of _"package.json"_ within _packageURL_.
+> 1. If the file at _pjsonURL_ does not exist, then
+>    1. Return **null**.
+> 1. If the file at _packageURL_ does not parse as valid JSON, then
+>    1. Throw an _Invalid Package Configuration_ error.
+> 1. Return the parsed JSON source of the file at _pjsonURL_.
+
+</details>
+
+### Customizing ESM specifier resolution algorithm
+
+The current specifier resolution does not support all default behavior of
+the CommonJS loader. One of the behavior differences is automatic resolution
+of file extensions and the ability to import directories that have an index
+file.
+
+The `--es-module-specifier-resolution=[mode]` flag can be used to customize
+the extension resolution algorithm. The default mode is `explicit`, which
+requires the full path to a module be provided to the loader. To enable the
+automatic extension resolution and importing from directories that include an
+index file use the `node` mode.
+
+```bash
+$ node --experimental-modules index.mjs
+success!
+$ node --experimental-modules index #Failure!
+Error: Cannot find module
+$ node --experimental-modules --es-module-specifier-resolution=node index
+success!
+```
+
+[`export`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export
+[`import`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import
+[`import()`]: #esm_import-expressions
+[`import.meta.url`]: #esm_import_meta
+[`module.createRequireFromPath()`]: modules.html#modules_module_createrequirefrompath_filename
+[CommonJS]: modules.html
+[ECMAScript-modules implementation]: https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md
 [Node.js EP for ES Modules]: https://github.com/nodejs/node-eps/blob/master/002-es-modules.md
-[addons]: addons.html
+[WHATWG JSON modules]: https://github.com/whatwg/html/issues/4315
 [dynamic instantiate hook]: #esm_dynamic_instantiate_hook
+[the official standard format]: https://tc39.github.io/ecma262/#sec-modules
diff --git a/doc/node.1 b/doc/node.1
index 7bcb1edc59..e2ac998cab 100644
--- a/doc/node.1
+++ b/doc/node.1
@@ -119,6 +119,15 @@ Enable FIPS-compliant crypto at startup.
 Requires Node.js to be built with
 .Sy ./configure --openssl-fips .
 .
+.It Fl -entry-type Ns = Ns Ar type
+Set the top-level module resolution type.
+.
+.It Fl -es-module-specifier-resolution
+Select extension resolution algorithm for ES Modules; either 'explicit' (default) or 'node'
+.
+.It Fl -experimental-json-modules
+Enable experimental JSON interop support for the ES Module loader.
+.
 .It Fl -experimental-modules
 Enable experimental ES module support and caching modules.
 .
diff --git a/lib/internal/bootstrap/pre_execution.js b/lib/internal/bootstrap/pre_execution.js
index 820d931575..20b362f213 100644
--- a/lib/internal/bootstrap/pre_execution.js
+++ b/lib/internal/bootstrap/pre_execution.js
@@ -323,6 +323,10 @@ function initializeESMLoader() {
     const userLoader = getOptionValue('--loader');
     // If --loader is specified, create a loader with user hooks. Otherwise
     // create the default loader.
+    if (userLoader) {
+      const { emitExperimentalWarning } = require('internal/util');
+      emitExperimentalWarning('--loader');
+    }
     esm.initializeLoader(process.cwd(), userLoader);
   }
 }
diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 42775691c3..e3347374cc 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -678,6 +678,24 @@ E('ERR_ENCODING_INVALID_ENCODED_DATA', function(encoding, ret) {
 }, TypeError);
 E('ERR_ENCODING_NOT_SUPPORTED', 'The "%s" encoding is not supported',
   RangeError);
+E('ERR_ENTRY_TYPE_MISMATCH', (filename, ext, typeFlag, conflict) => {
+  const typeString =
+    typeFlag === 'module' ? '--entry-type=module' : '--entry-type=commonjs';
+  // --entry-type mismatches file extension
+  if (conflict === 'extension') {
+    return `Extension ${ext} is not supported for ` +
+      `${typeString} loading ${filename}`;
+  }
+  assert(
+    conflict === 'scope',
+    '"conflict" value unknown. Set this argument to "extension" or "scope"'
+  );
+  // --entry-type mismatches package.json "type"
+  return `Cannot use ${typeString} because nearest parent package.json ` +
+    ((typeFlag === 'module') ?
+      'includes "type": "commonjs"' : 'includes "type": "module",') +
+    ` which controls the type to use for ${filename}`;
+}, TypeError);
 E('ERR_FALSY_VALUE_REJECTION', function(reason) {
   this.reason = reason;
   return 'Promise was rejected with falsy value';
@@ -864,6 +882,8 @@ E('ERR_INVALID_OPT_VALUE', (name, value) =>
   RangeError);
 E('ERR_INVALID_OPT_VALUE_ENCODING',
   'The value "%s" is invalid for option "encoding"', TypeError);
+E('ERR_INVALID_PACKAGE_CONFIG',
+  'Invalid package config in \'%s\' imported from %s', Error);
 E('ERR_INVALID_PERFORMANCE_MARK',
   'The "%s" performance mark has not been set', Error);
 E('ERR_INVALID_PROTOCOL',
@@ -958,11 +978,6 @@ E('ERR_MISSING_ARGS',
 E('ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK',
   'The ES Module loader may not return a format of \'dynamic\' when no ' +
   'dynamicInstantiate function was provided', Error);
-E('ERR_MISSING_MODULE', 'Cannot find module %s', Error);
-E('ERR_MODULE_RESOLUTION_LEGACY',
-  '%s not found by import in %s.' +
-    ' Legacy behavior in require() would have found it at %s',
-  Error);
 E('ERR_MULTIPLE_CALLBACK', 'Callback called multiple times', Error);
 E('ERR_NAPI_CONS_FUNCTION', 'Constructor must be a function', TypeError);
 E('ERR_NAPI_INVALID_DATAVIEW_ARGS',
@@ -1067,9 +1082,7 @@ E('ERR_UNHANDLED_ERROR',
 E('ERR_UNKNOWN_BUILTIN_MODULE', 'No such built-in module: %s', Error);
 E('ERR_UNKNOWN_CREDENTIAL', '%s identifier does not exist: %s', Error);
 E('ERR_UNKNOWN_ENCODING', 'Unknown encoding: %s', TypeError);
-
-// This should probably be a `TypeError`.
-E('ERR_UNKNOWN_FILE_EXTENSION', 'Unknown file extension: %s', Error);
+E('ERR_UNKNOWN_FILE_EXTENSION', 'Unknown file extension: %s', TypeError);
 E('ERR_UNKNOWN_MODULE_FORMAT', 'Unknown module format: %s', RangeError);
 E('ERR_UNKNOWN_SIGNAL', 'Unknown signal: %s', TypeError);
 
diff --git a/lib/internal/main/check_syntax.js b/lib/internal/main/check_syntax.js
index 7df70b2720..8c73d522ed 100644
--- a/lib/internal/main/check_syntax.js
+++ b/lib/internal/main/check_syntax.js
@@ -11,12 +11,18 @@ const {
   readStdin
 } = require('internal/process/execution');
 
-const CJSModule = require('internal/modules/cjs/loader');
+const { pathToFileURL } = require('url');
+
 const vm = require('vm');
 const {
   stripShebang, stripBOM
 } = require('internal/modules/cjs/helpers');
 
+let CJSModule;
+function CJSModuleInit() {
+  if (!CJSModule)
+    CJSModule = require('internal/modules/cjs/loader');
+}
 
 if (process.argv[1] && process.argv[1] !== '-') {
   // Expand process.argv[1] into a full path.
@@ -25,7 +31,7 @@ if (process.argv[1] && process.argv[1] !== '-') {
 
   // TODO(joyeecheung): not every one of these are necessary
   prepareMainThreadExecution();
-
+  CJSModuleInit();
   // Read the source.
   const filename = CJSModule._resolveFilename(process.argv[1]);
 
@@ -34,20 +40,40 @@ if (process.argv[1] && process.argv[1] !== '-') {
 
   markBootstrapComplete();
 
-  checkScriptSyntax(source, filename);
+  checkSyntax(source, filename);
 } else {
   // TODO(joyeecheung): not every one of these are necessary
   prepareMainThreadExecution();
+  CJSModuleInit();
   markBootstrapComplete();
 
   readStdin((code) => {
-    checkScriptSyntax(code, '[stdin]');
+    checkSyntax(code, '[stdin]');
   });
 }
 
-function checkScriptSyntax(source, filename) {
+function checkSyntax(source, filename) {
   // Remove Shebang.
   source = stripShebang(source);
+
+  const { getOptionValue } = require('internal/options');
+  const experimentalModules = getOptionValue('--experimental-modules');
+  if (experimentalModules) {
+    let isModule = false;
+    if (filename === '[stdin]' || filename === '[eval]') {
+      isModule = getOptionValue('--entry-type') === 'module';
+    } else {
+      const resolve = require('internal/modules/esm/default_resolve');
+      const { format } = resolve(pathToFileURL(filename).toString());
+      isModule = format === 'module';
+    }
+    if (isModule) {
+      const { ModuleWrap } = internalBinding('module_wrap');
+      new ModuleWrap(source, filename);
+      return;
+    }
+  }
+
   // Remove BOM.
   source = stripBOM(source);
   // Wrap it.
diff --git a/lib/internal/main/eval_stdin.js b/lib/internal/main/eval_stdin.js
index 2a2ef6d38a..4face9e61e 100644
--- a/lib/internal/main/eval_stdin.js
+++ b/lib/internal/main/eval_stdin.js
@@ -7,6 +7,7 @@ const {
 } = require('internal/bootstrap/pre_execution');
 
 const {
+  evalModule,
   evalScript,
   readStdin
 } = require('internal/process/execution');
@@ -16,5 +17,8 @@ markBootstrapComplete();
 
 readStdin((code) => {
   process._eval = code;
-  evalScript('[stdin]', process._eval, process._breakFirstLine);
+  if (require('internal/options').getOptionValue('--entry-type') === 'module')
+    evalModule(process._eval);
+  else
+    evalScript('[stdin]', process._eval, process._breakFirstLine);
 });
diff --git a/lib/internal/main/eval_string.js b/lib/internal/main/eval_string.js
index 953fab386d..b032281925 100644
--- a/lib/internal/main/eval_string.js
+++ b/lib/internal/main/eval_string.js
@@ -6,11 +6,15 @@
 const {
   prepareMainThreadExecution
 } = require('internal/bootstrap/pre_execution');
-const { evalScript } = require('internal/process/execution');
+const { evalModule, evalScript } = require('internal/process/execution');
 const { addBuiltinLibsToObject } = require('internal/modules/cjs/helpers');
 
-const source = require('internal/options').getOptionValue('--eval');
+const { getOptionValue } = require('internal/options');
+const source = getOptionValue('--eval');
 prepareMainThreadExecution();
 addBuiltinLibsToObject(global);
 markBootstrapComplete();
-evalScript('[eval]', source, process._breakFirstLine);
+if (getOptionValue('--entry-type') === 'module')
+  evalModule(source);
+else
+  evalScript('[eval]', source, process._breakFirstLine);
diff --git a/lib/internal/main/repl.js b/lib/internal/main/repl.js
index e6b9885351..c2bf54f8bb 100644
--- a/lib/internal/main/repl.js
+++ b/lib/internal/main/repl.js
@@ -13,6 +13,12 @@ const {
 
 prepareMainThreadExecution();
 
+// --entry-type flag not supported in REPL
+if (require('internal/options').getOptionValue('--entry-type')) {
+  console.error('Cannot specify --entry-type for REPL');
+  process.exit(1);
+}
+
 const cliRepl = require('internal/repl');
 cliRepl.createInternalRepl(process.env, (err, repl) => {
   if (err) {
diff --git a/lib/internal/modules/cjs/loader.js b/lib/internal/modules/cjs/loader.js
index b7486db6e4..3d68f8fc62 100644
--- a/lib/internal/modules/cjs/loader.js
+++ b/lib/internal/modules/cjs/loader.js
@@ -896,9 +896,11 @@ Module.runMain = function() {
     .catch((e) => {
       internalBinding('task_queue').triggerFatalException(e);
     });
-  } else {
-    Module._load(process.argv[1], null, true);
+    // Handle any nextTicks added in the first tick of the program
+    process._tickCallback();
+    return;
   }
+  Module._load(process.argv[1], null, true);
   // Handle any nextTicks added in the first tick of the program
   process._tickCallback();
 };
diff --git a/lib/internal/modules/esm/default_resolve.js b/lib/internal/modules/esm/default_resolve.js
index 33366f0069..8da24cf5b3 100644
--- a/lib/internal/modules/esm/default_resolve.js
+++ b/lib/internal/modules/esm/default_resolve.js
@@ -1,57 +1,54 @@
 'use strict';
 
-const { URL } = require('url');
-const CJSmodule = require('internal/modules/cjs/loader');
 const internalFS = require('internal/fs/utils');
 const { NativeModule } = require('internal/bootstrap/loaders');
 const { extname } = require('path');
 const { realpathSync } = require('fs');
 const { getOptionValue } = require('internal/options');
+
 const preserveSymlinks = getOptionValue('--preserve-symlinks');
 const preserveSymlinksMain = getOptionValue('--preserve-symlinks-main');
-const {
-  ERR_MISSING_MODULE,
-  ERR_MODULE_RESOLUTION_LEGACY,
-  ERR_UNKNOWN_FILE_EXTENSION
-} = require('internal/errors').codes;
-const { resolve: moduleWrapResolve } = internalBinding('module_wrap');
-const StringStartsWith = Function.call.bind(String.prototype.startsWith);
+const experimentalJsonModules = getOptionValue('--experimental-json-modules');
+const typeFlag = getOptionValue('--entry-type');
+
+const { resolve: moduleWrapResolve,
+        getPackageType } = internalBinding('module_wrap');
 const { pathToFileURL, fileURLToPath } = require('internal/url');
+const { ERR_ENTRY_TYPE_MISMATCH,
+        ERR_UNKNOWN_FILE_EXTENSION } = require('internal/errors').codes;
 
 const realpathCache = new Map();
 
-function search(target, base) {
-  if (base === undefined) {
-    // We cannot search without a base.
-    throw new ERR_MISSING_MODULE(target);
-  }
-  try {
-    return moduleWrapResolve(target, base);
-  } catch (e) {
-    e.stack; // cause V8 to generate stack before rethrow
-    let error = e;
-    try {
-      const questionedBase = new URL(base);
-      const tmpMod = new CJSmodule(questionedBase.pathname, null);
-      tmpMod.paths = CJSmodule._nodeModulePaths(
-        new URL('./', questionedBase).pathname);
-      const found = CJSmodule._resolveFilename(target, tmpMod);
-      error = new ERR_MODULE_RESOLUTION_LEGACY(target, base, found);
-    } catch {
-      // ignore
-    }
-    throw error;
-  }
-}
+// const TYPE_NONE = 0;
+const TYPE_COMMONJS = 1;
+const TYPE_MODULE = 2;
 
 const extensionFormatMap = {
   '__proto__': null,
-  '.mjs': 'esm',
-  '.json': 'json',
-  '.node': 'addon',
-  '.js': 'cjs'
+  '.cjs': 'commonjs',
+  '.js': 'module',
+  '.mjs': 'module'
 };
 
+const legacyExtensionFormatMap = {
+  '__proto__': null,
+  '.cjs': 'commonjs',
+  '.js': 'commonjs',
+  '.json': 'commonjs',
+  '.mjs': 'module',
+  '.node': 'commonjs'
+};
+
+if (experimentalJsonModules) {
+  // This is a total hack
+  Object.assign(extensionFormatMap, {
+    '.json': 'json'
+  });
+  Object.assign(legacyExtensionFormatMap, {
+    '.json': 'json'
+  });
+}
+
 function resolve(specifier, parentURL) {
   if (NativeModule.canBeRequiredByUsers(specifier)) {
     return {
@@ -60,21 +57,11 @@ function resolve(specifier, parentURL) {
     };
   }
 
-  let url;
-  try {
-    url = search(specifier,
-                 parentURL || pathToFileURL(`${process.cwd()}/`).href);
-  } catch (e) {
-    if (typeof e.message === 'string' &&
-        StringStartsWith(e.message, 'Cannot find module')) {
-      e.code = 'MODULE_NOT_FOUND';
-      // TODO: also add e.requireStack to match behavior with CJS
-      // MODULE_NOT_FOUND.
-    }
-    throw e;
-  }
-
   const isMain = parentURL === undefined;
+  if (isMain)
+    parentURL = pathToFileURL(`${process.cwd()}/`).href;
+
+  let url = moduleWrapResolve(specifier, parentURL);
 
   if (isMain ? !preserveSymlinksMain : !preserveSymlinks) {
     const real = realpathSync(fileURLToPath(url), {
@@ -86,19 +73,40 @@ function resolve(specifier, parentURL) {
     url.hash = old.hash;
   }
 
+  const type = getPackageType(url.href);
+
   const ext = extname(url.pathname);
+  const extMap =
+      type !== TYPE_MODULE ? legacyExtensionFormatMap : extensionFormatMap;
+  let format = extMap[ext];
 
-  let format = extensionFormatMap[ext];
+  if (isMain && typeFlag) {
+    // Conflict between explicit extension (.mjs, .cjs) and --entry-type
+    if (ext === '.cjs' && typeFlag === 'module' ||
+        ext === '.mjs' && typeFlag === 'commonjs') {
+      throw new ERR_ENTRY_TYPE_MISMATCH(
+        fileURLToPath(url), ext, typeFlag, 'extension');
+    }
+
+    // Conflict between package scope type and --entry-type
+    if (ext === '.js') {
+      if (type === TYPE_MODULE && typeFlag === 'commonjs' ||
+          type === TYPE_COMMONJS && typeFlag === 'module') {
+        throw new ERR_ENTRY_TYPE_MISMATCH(
+          fileURLToPath(url), ext, typeFlag, 'scope');
+      }
+    }
+  }
   if (!format) {
-    if (isMain)
-      format = 'cjs';
+    if (isMain && typeFlag)
+      format = typeFlag;
+    else if (isMain)
+      format = type === TYPE_MODULE ? 'module' : 'commonjs';
     else
-      throw new ERR_UNKNOWN_FILE_EXTENSION(url.pathname);
+      throw new ERR_UNKNOWN_FILE_EXTENSION(fileURLToPath(url),
+                                           fileURLToPath(parentURL));
   }
-
   return { url: `${url}`, format };
 }
 
 module.exports = resolve;
-// exported for tests
-module.exports.search = search;
diff --git a/lib/internal/modules/esm/loader.js b/lib/internal/modules/esm/loader.js
index aff1211368..465775f56f 100644
--- a/lib/internal/modules/esm/loader.js
+++ b/lib/internal/modules/esm/loader.js
@@ -11,10 +11,12 @@ const { URL } = require('url');
 const { validateString } = require('internal/validators');
 const ModuleMap = require('internal/modules/esm/module_map');
 const ModuleJob = require('internal/modules/esm/module_job');
+
 const defaultResolve = require('internal/modules/esm/default_resolve');
 const createDynamicModule = require(
   'internal/modules/esm/create_dynamic_module');
-const translators = require('internal/modules/esm/translators');
+const { translators } = require('internal/modules/esm/translators');
+const { ModuleWrap } = internalBinding('module_wrap');
 
 const FunctionBind = Function.call.bind(Function.prototype.bind);
 
@@ -32,6 +34,9 @@ class Loader {
     // Registry of loaded modules, akin to `require.cache`
     this.moduleMap = new ModuleMap();
 
+    // Map of already-loaded CJS modules to use
+    this.cjsCache = new Map();
+
     // The resolver has the signature
     //   (specifier : string, parentURL : string, defaultResolve)
     //       -> Promise<{ url : string, format: string }>
@@ -48,6 +53,8 @@ class Loader {
     // an object with the same keys as `exports`, whose values are get/set
     // functions for the actual exported values.
     this._dynamicInstantiate = undefined;
+    // The index for assigning unique URLs to anonymous module evaluation
+    this.evalIndex = 0;
   }
 
   async resolve(specifier, parentURL) {
@@ -95,9 +102,25 @@ class Loader {
     return { url, format };
   }
 
+  async eval(source, url = `eval:${++this.evalIndex}`) {
+    const evalInstance = async (url) => {
+      return {
+        module: new ModuleWrap(source, url),
+        reflect: undefined
+      };
+    };
+    const job = new ModuleJob(this, url, evalInstance, false);
+    this.moduleMap.set(url, job);
+    const { module, result } = await job.run();
+    return {
+      namespace: module.namespace(),
+      result
+    };
+  }
+
   async import(specifier, parent) {
     const job = await this.getModuleJob(specifier, parent);
-    const module = await job.run();
+    const { module } = await job.run();
     return module.namespace();
   }
 
@@ -143,4 +166,4 @@ class Loader {
 
 Object.setPrototypeOf(Loader.prototype, null);
 
-module.exports = Loader;
+exports.Loader = Loader;
diff --git a/lib/internal/modules/esm/module_job.js b/lib/internal/modules/esm/module_job.js
index 016495096c..5666032df1 100644
--- a/lib/internal/modules/esm/module_job.js
+++ b/lib/internal/modules/esm/module_job.js
@@ -23,7 +23,7 @@ class ModuleJob {
 
     // This is a Promise<{ module, reflect }>, whose fields will be copied
     // onto `this` by `link()` below once it has been resolved.
-    this.modulePromise = moduleProvider(url, isMain);
+    this.modulePromise = moduleProvider.call(loader, url, isMain);
     this.module = undefined;
     this.reflect = undefined;
 
@@ -101,8 +101,9 @@ class ModuleJob {
 
   async run() {
     const module = await this.instantiate();
-    module.evaluate(-1, false);
-    return module;
+    const timeout = -1;
+    const breakOnSigint = false;
+    return { module, result: module.evaluate(timeout, breakOnSigint) };
   }
 }
 Object.setPrototypeOf(ModuleJob.prototype, null);
diff --git a/lib/internal/modules/esm/translators.js b/lib/internal/modules/esm/translators.js
index de09910872..172569fb04 100644
--- a/lib/internal/modules/esm/translators.js
+++ b/lib/internal/modules/esm/translators.js
@@ -11,14 +11,10 @@ const internalURLModule = require('internal/url');
 const createDynamicModule = require(
   'internal/modules/esm/create_dynamic_module');
 const fs = require('fs');
-const { _makeLong } = require('path');
 const {
   SafeMap,
-  JSON,
-  FunctionPrototype,
-  StringPrototype
 } = primordials;
-const { URL } = require('url');
+const { fileURLToPath, URL } = require('url');
 const { debuglog } = require('internal/util/debuglog');
 const { promisify } = require('internal/util');
 const esmLoader = require('internal/process/esm_loader');
@@ -26,14 +22,13 @@ const {
   ERR_UNKNOWN_BUILTIN_MODULE
 } = require('internal/errors').codes;
 const readFileAsync = promisify(fs.readFile);
-const readFileSync = fs.readFileSync;
-const StringReplace = FunctionPrototype.call.bind(StringPrototype.replace);
+const StringReplace = Function.call.bind(String.prototype.replace);
 const JsonParse = JSON.parse;
 
 const debug = debuglog('esm');
 
 const translators = new SafeMap();
-module.exports = translators;
+exports.translators = translators;
 
 function initializeImportMeta(meta, { url }) {
   meta.url = url;
@@ -45,7 +40,7 @@ async function importModuleDynamically(specifier, { url }) {
 }
 
 // Strategy for loading a standard JavaScript module
-translators.set('esm', async (url) => {
+translators.set('module', async function moduleStrategy(url) {
   const source = `${await readFileAsync(new URL(url))}`;
   debug(`Translating StandardModule ${url}`);
   const module = new ModuleWrap(stripShebang(source), url);
@@ -62,9 +57,14 @@ translators.set('esm', async (url) => {
 // Strategy for loading a node-style CommonJS module
 const isWindows = process.platform === 'win32';
 const winSepRegEx = /\//g;
-translators.set('cjs', async (url, isMain) => {
+translators.set('commonjs', async function commonjsStrategy(url, isMain) {
   debug(`Translating CJSModule ${url}`);
   const pathname = internalURLModule.fileURLToPath(new URL(url));
+  const cached = this.cjsCache.get(url);
+  if (cached) {
+    this.cjsCache.delete(url);
+    return cached;
+  }
   const module = CJSModule._cache[
     isWindows ? StringReplace(pathname, winSepRegEx, '\\') : pathname];
   if (module && module.loaded) {
@@ -84,7 +84,7 @@ translators.set('cjs', async (url, isMain) => {
 
 // Strategy for loading a node builtin CommonJS module that isn't
 // through normal resolution
-translators.set('builtin', async (url) => {
+translators.set('builtin', async function builtinStrategy(url) {
   debug(`Translating BuiltinModule ${url}`);
   // Slice 'node:' scheme
   const id = url.slice(5);
@@ -103,31 +103,38 @@ translators.set('builtin', async (url) => {
     });
 });
 
-// Strategy for loading a node native module
-translators.set('addon', async (url) => {
-  debug(`Translating NativeModule ${url}`);
-  return createDynamicModule(['default'], url, (reflect) => {
-    debug(`Loading NativeModule ${url}`);
-    const module = { exports: {} };
-    const pathname = internalURLModule.fileURLToPath(new URL(url));
-    process.dlopen(module, _makeLong(pathname));
-    reflect.exports.default.set(module.exports);
-  });
-});
-
 // Strategy for loading a JSON file
-translators.set('json', async (url) => {
+translators.set('json', async function jsonStrategy(url) {
   debug(`Translating JSONModule ${url}`);
-  return createDynamicModule(['default'], url, (reflect) => {
-    debug(`Loading JSONModule ${url}`);
-    const pathname = internalURLModule.fileURLToPath(new URL(url));
-    const content = readFileSync(pathname, 'utf8');
-    try {
-      const exports = JsonParse(stripBOM(content));
+  debug(`Loading JSONModule ${url}`);
+  const pathname = fileURLToPath(url);
+  const modulePath = isWindows ?
+    StringReplace(pathname, winSepRegEx, '\\') : pathname;
+  let module = CJSModule._cache[modulePath];
+  if (module && module.loaded) {
+    const exports = module.exports;
+    return createDynamicModule(['default'], url, (reflect) => {
       reflect.exports.default.set(exports);
-    } catch (err) {
-      err.message = pathname + ': ' + err.message;
-      throw err;
-    }
+    });
+  }
+  const content = await readFileAsync(pathname, 'utf-8');
+  try {
+    const exports = JsonParse(stripBOM(content));
+    module = {
+      exports,
+      loaded: true
+    };
+  } catch (err) {
+    // TODO (BridgeAR): We could add a NodeCore error that wraps the JSON
+    // parse error instead of just manipulating the original error message.
+    // That would allow to add further properties and maybe additional
+    // debugging information.
+    err.message = pathname + ': ' + err.message;
+    throw err;
+  }
+  CJSModule._cache[modulePath] = module;
+  return createDynamicModule(['default'], url, (reflect) => {
+    debug(`Parsing JSONModule ${url}`);
+    reflect.exports.default.set(module.exports);
   });
 });
diff --git a/lib/internal/process/esm_loader.js b/lib/internal/process/esm_loader.js
index 0b7f1be6ff..6225ea81ab 100644
--- a/lib/internal/process/esm_loader.js
+++ b/lib/internal/process/esm_loader.js
@@ -3,15 +3,15 @@
 const {
   callbackMap,
 } = internalBinding('module_wrap');
+const {
+  ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
+} = require('internal/errors').codes;
 
+const { Loader } = require('internal/modules/esm/loader');
 const { pathToFileURL } = require('internal/url');
-const Loader = require('internal/modules/esm/loader');
 const {
   wrapToModuleMap,
 } = require('internal/vm/source_text_module');
-const {
-  ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
-} = require('internal/errors').codes;
 
 exports.initializeImportMetaObject = function(wrap, meta) {
   if (callbackMap.has(wrap)) {
@@ -34,9 +34,7 @@ exports.importModuleDynamicallyCallback = async function(wrap, specifier) {
 };
 
 let loaderResolve;
-exports.loaderPromise = new Promise((resolve, reject) => {
-  loaderResolve = resolve;
-});
+exports.loaderPromise = new Promise((resolve) => loaderResolve = resolve);
 
 exports.ESMLoader = undefined;
 
diff --git a/lib/internal/process/execution.js b/lib/internal/process/execution.js
index 7118dbf3ad..070410ef6f 100644
--- a/lib/internal/process/execution.js
+++ b/lib/internal/process/execution.js
@@ -33,6 +33,24 @@ function tryGetCwd() {
   }
 }
 
+function evalModule(source) {
+  const { decorateErrorStack } = require('internal/util');
+  const asyncESM = require('internal/process/esm_loader');
+  asyncESM.loaderPromise.then(async (loader) => {
+    const { result } = await loader.eval(source);
+    if (require('internal/options').getOptionValue('--print')) {
+      console.log(result);
+    }
+  })
+  .catch((e) => {
+    decorateErrorStack(e);
+    console.error(e);
+    process.exit(1);
+  });
+  // Handle any nextTicks added in the first tick of the program.
+  process._tickCallback();
+}
+
 function evalScript(name, body, breakFirstLine) {
   const CJSModule = require('internal/modules/cjs/loader');
   const { kVmBreakFirstLineSymbol } = require('internal/util');
@@ -176,6 +194,7 @@ function readStdin(callback) {
 module.exports = {
   readStdin,
   tryGetCwd,
+  evalModule,
   evalScript,
   fatalException: createFatalException(),
   setUncaughtExceptionCaptureCallback,
diff --git a/src/env.h b/src/env.h
index 55018b6d40..743c236827 100644
--- a/src/env.h
+++ b/src/env.h
@@ -77,11 +77,13 @@ struct PackageConfig {
   enum class Exists { Yes, No };
   enum class IsValid { Yes, No };
   enum class HasMain { Yes, No };
+  enum PackageType : uint32_t { None = 0, CommonJS, Module };
 
-  Exists exists;
-  IsValid is_valid;
-  HasMain has_main;
-  std::string main;
+  const Exists exists;
+  const IsValid is_valid;
+  const HasMain has_main;
+  const std::string main;
+  const PackageType type;
 };
 }  // namespace loader
 
@@ -141,6 +143,7 @@ constexpr size_t kFsStatsBufferLength = kFsStatsFieldsNumber * 2;
   V(channel_string, "channel")                                                 \
   V(chunks_sent_since_last_write_string, "chunksSentSinceLastWrite")           \
   V(code_string, "code")                                                       \
+  V(commonjs_string, "commonjs")                                               \
   V(config_string, "config")                                                   \
   V(constants_string, "constants")                                             \
   V(crypto_dsa_string, "dsa")                                                  \
diff --git a/src/module_wrap.cc b/src/module_wrap.cc
index 56149d0cc7..622deed45f 100644
--- a/src/module_wrap.cc
+++ b/src/module_wrap.cc
@@ -29,7 +29,6 @@ using v8::HandleScope;
 using v8::Integer;
 using v8::IntegrityLevel;
 using v8::Isolate;
-using v8::JSON;
 using v8::Just;
 using v8::Local;
 using v8::Maybe;
@@ -46,7 +45,13 @@ using v8::String;
 using v8::Undefined;
 using v8::Value;
 
-static const char* const EXTENSIONS[] = {".mjs", ".js", ".json", ".node"};
+static const char* const EXTENSIONS[] = {
+  ".mjs",
+  ".cjs",
+  ".js",
+  ".json",
+  ".node"
+};
 
 ModuleWrap::ModuleWrap(Environment* env,
                        Local<Object> object,
@@ -471,100 +476,233 @@ std::string ReadFile(uv_file file) {
   return contents;
 }
 
-enum CheckFileOptions {
-  LEAVE_OPEN_AFTER_CHECK,
-  CLOSE_AFTER_CHECK
+enum DescriptorType {
+  FILE,
+  DIRECTORY,
+  NONE
 };
 
-Maybe<uv_file> CheckFile(const std::string& path,
-                         CheckFileOptions opt = CLOSE_AFTER_CHECK) {
+// When DescriptorType cache is added, this can also return
+// Nothing for the "null" cache entries.
+inline Maybe<uv_file> OpenDescriptor(const std::string& path) {
   uv_fs_t fs_req;
-  if (path.empty()) {
-    return Nothing<uv_file>();
-  }
-
   uv_file fd = uv_fs_open(nullptr, &fs_req, path.c_str(), O_RDONLY, 0, nullptr);
   uv_fs_req_cleanup(&fs_req);
+  if (fd < 0) return Nothing<uv_file>();
+  return Just(fd);
+}
 
-  if (fd < 0) {
-    return Nothing<uv_file>();
-  }
-
-  uv_fs_fstat(nullptr, &fs_req, fd, nullptr);
-  uint64_t is_directory = fs_req.statbuf.st_mode & S_IFDIR;
+inline void CloseDescriptor(uv_file fd) {
+  uv_fs_t fs_req;
+  uv_fs_close(nullptr, &fs_req, fd, nullptr);
   uv_fs_req_cleanup(&fs_req);
+}
 
-  if (is_directory) {
-    CHECK_EQ(0, uv_fs_close(nullptr, &fs_req, fd, nullptr));
+inline DescriptorType CheckDescriptorAtFile(uv_file fd) {
+  uv_fs_t fs_req;
+  int rc = uv_fs_fstat(nullptr, &fs_req, fd, nullptr);
+  if (rc == 0) {
+    uint64_t is_directory = fs_req.statbuf.st_mode & S_IFDIR;
     uv_fs_req_cleanup(&fs_req);
-    return Nothing<uv_file>();
+    return is_directory ? DIRECTORY : FILE;
   }
+  uv_fs_req_cleanup(&fs_req);
+  return NONE;
+}
 
-  if (opt == CLOSE_AFTER_CHECK) {
-    CHECK_EQ(0, uv_fs_close(nullptr, &fs_req, fd, nullptr));
-    uv_fs_req_cleanup(&fs_req);
-  }
+// TODO(@guybedford): Add a DescriptorType cache layer here.
+// Should be directory based -> if path/to/dir doesn't exist
+// then the cache should early-fail any path/to/dir/file check.
+DescriptorType CheckDescriptorAtPath(const std::string& path) {
+  Maybe<uv_file> fd = OpenDescriptor(path);
+  if (fd.IsNothing()) return NONE;
+  DescriptorType type = CheckDescriptorAtFile(fd.FromJust());
+  CloseDescriptor(fd.FromJust());
+  return type;
+}
 
-  return Just(fd);
+Maybe<std::string> ReadIfFile(const std::string& path) {
+  Maybe<uv_file> fd = OpenDescriptor(path);
+  if (fd.IsNothing()) return Nothing<std::string>();
+  DescriptorType type = CheckDescriptorAtFile(fd.FromJust());
+  if (type != FILE) return Nothing<std::string>();
+  std::string source = ReadFile(fd.FromJust());
+  CloseDescriptor(fd.FromJust());
+  return Just(source);
 }
 
 using Exists = PackageConfig::Exists;
 using IsValid = PackageConfig::IsValid;
 using HasMain = PackageConfig::HasMain;
+using PackageType = PackageConfig::PackageType;
 
-const PackageConfig& GetPackageConfig(Environment* env,
-                                      const std::string& path) {
+Maybe<const PackageConfig*> GetPackageConfig(Environment* env,
+                                             const std::string& path,
+                                             const URL& base) {
   auto existing = env->package_json_cache.find(path);
   if (existing != env->package_json_cache.end()) {
-    return existing->second;
+    const PackageConfig* pcfg = &existing->second;
+    if (pcfg->is_valid == IsValid::No) {
+      std::string msg = "Invalid JSON in '" + path +
+        "' imported from " + base.ToFilePath();
+      node::THROW_ERR_INVALID_PACKAGE_CONFIG(env, msg.c_str());
+      return Nothing<const PackageConfig*>();
+    }
+    return Just(pcfg);
   }
-  Maybe<uv_file> check = CheckFile(path, LEAVE_OPEN_AFTER_CHECK);
-  if (check.IsNothing()) {
+
+  Maybe<std::string> source = ReadIfFile(path);
+
+  if (source.IsNothing()) {
     auto entry = env->package_json_cache.emplace(path,
-        PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "" });
-    return entry.first->second;
+        PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "",
+                        PackageType::None });
+    return Just(&entry.first->second);
   }
 
+  std::string pkg_src = source.FromJust();
+
   Isolate* isolate = env->isolate();
   v8::HandleScope handle_scope(isolate);
 
-  std::string pkg_src = ReadFile(check.FromJust());
-  uv_fs_t fs_req;
-  CHECK_EQ(0, uv_fs_close(nullptr, &fs_req, check.FromJust(), nullptr));
-  uv_fs_req_cleanup(&fs_req);
-
-  Local<String> src;
-  if (!String::NewFromUtf8(isolate,
-                           pkg_src.c_str(),
-                           v8::NewStringType::kNormal,
-                           pkg_src.length()).ToLocal(&src)) {
-    auto entry = env->package_json_cache.emplace(path,
-        PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "" });
-    return entry.first->second;
-  }
-
-  Local<Value> pkg_json_v;
   Local<Object> pkg_json;
-
-  if (!JSON::Parse(env->context(), src).ToLocal(&pkg_json_v) ||
-      !pkg_json_v->ToObject(env->context()).ToLocal(&pkg_json)) {
-    auto entry = env->package_json_cache.emplace(path,
-        PackageConfig { Exists::Yes, IsValid::No, HasMain::No, "" });
-    return entry.first->second;
+  {
+    Local<Value> src;
+    Local<Value> pkg_json_v;
+    Local<Context> context = env->context();
+
+    if (!ToV8Value(context, pkg_src).ToLocal(&src) ||
+        !v8::JSON::Parse(context, src.As<String>()).ToLocal(&pkg_json_v) ||
+        !pkg_json_v->ToObject(context).ToLocal(&pkg_json)) {
+      env->package_json_cache.emplace(path,
+          PackageConfig { Exists::Yes, IsValid::No, HasMain::No, "",
+                          PackageType::None });
+      std::string msg = "Invalid JSON in '" + path +
+          "' imported from " + base.ToFilePath();
+      node::THROW_ERR_INVALID_PACKAGE_CONFIG(env, msg.c_str());
+      return Nothing<const PackageConfig*>();
+    }
   }
 
   Local<Value> pkg_main;
   HasMain has_main = HasMain::No;
   std::string main_std;
   if (pkg_json->Get(env->context(), env->main_string()).ToLocal(&pkg_main)) {
-    has_main = HasMain::Yes;
+    if (pkg_main->IsString()) {
+      has_main = HasMain::Yes;
+    }
     Utf8Value main_utf8(isolate, pkg_main);
     main_std.assign(std::string(*main_utf8, main_utf8.length()));
   }
 
+  PackageType pkg_type = PackageType::None;
+  Local<Value> type_v;
+  if (pkg_json->Get(env->context(), env->type_string()).ToLocal(&type_v)) {
+    if (type_v->StrictEquals(env->module_string())) {
+      pkg_type = PackageType::Module;
+    } else if (type_v->StrictEquals(env->commonjs_string())) {
+      pkg_type = PackageType::CommonJS;
+    }
+    // ignore unknown types for forwards compatibility
+  }
+
+  Local<Value> exports_v;
+  if (pkg_json->Get(env->context(),
+      env->exports_string()).ToLocal(&exports_v) &&
+      (exports_v->IsObject() || exports_v->IsString() ||
+      exports_v->IsBoolean())) {
+    Persistent<Value> exports;
+    exports.Reset(env->isolate(), exports_v);
+
+    auto entry = env->package_json_cache.emplace(path,
+        PackageConfig { Exists::Yes, IsValid::Yes, has_main, main_std,
+                        pkg_type });
+    return Just(&entry.first->second);
+  }
+
   auto entry = env->package_json_cache.emplace(path,
-      PackageConfig { Exists::Yes, IsValid::Yes, has_main, main_std });
-  return entry.first->second;
+      PackageConfig { Exists::Yes, IsValid::Yes, has_main, main_std,
+                      pkg_type });
+  return Just(&entry.first->second);
+}
+
+Maybe<const PackageConfig*> GetPackageScopeConfig(Environment* env,
+                                                  const URL& resolved,
+                                                  const URL& base) {
+  URL pjson_url("./package.json", &resolved);
+  while (true) {
+    Maybe<const PackageConfig*> pkg_cfg =
+        GetPackageConfig(env, pjson_url.ToFilePath(), base);
+    if (pkg_cfg.IsNothing()) return pkg_cfg;
+    if (pkg_cfg.FromJust()->exists == Exists::Yes) return pkg_cfg;
+
+    URL last_pjson_url = pjson_url;
+    pjson_url = URL("../package.json", pjson_url);
+
+    // Terminates at root where ../package.json equals ../../package.json
+    // (can't just check "/package.json" for Windows support).
+    if (pjson_url.path() == last_pjson_url.path()) {
+      auto entry = env->package_json_cache.emplace(pjson_url.ToFilePath(),
+          PackageConfig { Exists::No, IsValid::Yes, HasMain::No, "",
+                          PackageType::None });
+      const PackageConfig* pcfg = &entry.first->second;
+      return Just(pcfg);
+    }
+  }
+}
+
+/*
+ * Legacy CommonJS main resolution:
+ * 1. let M = pkg_url + (json main field)
+ * 2. TRY(M, M.js, M.json, M.node)
+ * 3. TRY(M/index.js, M/index.json, M/index.node)
+ * 4. TRY(pkg_url/index.js, pkg_url/index.json, pkg_url/index.node)
+ * 5. NOT_FOUND
+ */
+inline bool FileExists(const URL& url) {
+  return CheckDescriptorAtPath(url.ToFilePath()) == FILE;
+}
+Maybe<URL> LegacyMainResolve(const URL& pjson_url,
+                             const PackageConfig& pcfg) {
+  URL guess;
+  if (pcfg.has_main == HasMain::Yes) {
+    // Note: fs check redundances will be handled by Descriptor cache here.
+    if (FileExists(guess = URL("./" + pcfg.main, pjson_url))) {
+      return Just(guess);
+    }
+    if (FileExists(guess = URL("./" + pcfg.main + ".js", pjson_url))) {
+      return Just(guess);
+    }
+    if (FileExists(guess = URL("./" + pcfg.main + ".json", pjson_url))) {
+      return Just(guess);
+    }
+    if (FileExists(guess = URL("./" + pcfg.main + ".node", pjson_url))) {
+      return Just(guess);
+    }
+    if (FileExists(guess = URL("./" + pcfg.main + "/index.js", pjson_url))) {
+      return Just(guess);
+    }
+    // Such stat.
+    if (FileExists(guess = URL("./" + pcfg.main + "/index.json", pjson_url))) {
+      return Just(guess);
+    }
+    if (FileExists(guess = URL("./" + pcfg.main + "/index.node", pjson_url))) {
+      return Just(guess);
+    }
+    // Fallthrough.
+  }
+  if (FileExists(guess = URL("./index.js", pjson_url))) {
+    return Just(guess);
+  }
+  // So fs.
+  if (FileExists(guess = URL("./index.json", pjson_url))) {
+    return Just(guess);
+  }
+  if (FileExists(guess = URL("./index.node", pjson_url))) {
+    return Just(guess);
+  }
+  // Not found.
+  return Nothing<URL>();
 }
 
 enum ResolveExtensionsOptions {
@@ -575,17 +713,14 @@ enum ResolveExtensionsOptions {
 template <ResolveExtensionsOptions options>
 Maybe<URL> ResolveExtensions(const URL& search) {
   if (options == TRY_EXACT_NAME) {
-    std::string filePath = search.ToFilePath();
-    Maybe<uv_file> check = CheckFile(filePath);
-    if (!check.IsNothing()) {
+    if (FileExists(search)) {
       return Just(search);
     }
   }
 
   for (const char* extension : EXTENSIONS) {
     URL guess(search.path() + extension, &search);
-    Maybe<uv_file> check = CheckFile(guess.ToFilePath());
-    if (!check.IsNothing()) {
+    if (FileExists(guess)) {
       return Just(guess);
     }
   }
@@ -597,93 +732,150 @@ inline Maybe<URL> ResolveIndex(const URL& search) {
   return ResolveExtensions<ONLY_VIA_EXTENSIONS>(URL("index", search));
 }
 
-Maybe<URL> ResolveMain(Environment* env, const URL& search) {
-  URL pkg("package.json", &search);
-
-  const PackageConfig& pjson =
-      GetPackageConfig(env, pkg.ToFilePath());
-  // Note invalid package.json should throw in resolver
-  // currently we silently ignore which is incorrect
-  if (pjson.exists == Exists::No ||
-      pjson.is_valid == IsValid::No ||
-      pjson.has_main == HasMain::No) {
+Maybe<URL> FinalizeResolution(Environment* env,
+                              const URL& resolved,
+                              const URL& base) {
+  if (env->options()->es_module_specifier_resolution == "node") {
+    Maybe<URL> file = ResolveExtensions<TRY_EXACT_NAME>(resolved);
+    if (!file.IsNothing()) {
+      return file;
+    }
+    if (resolved.path().back() != '/') {
+      file = ResolveIndex(URL(resolved.path() + "/", &base));
+    } else {
+      file = ResolveIndex(resolved);
+    }
+    if (!file.IsNothing()) {
+      return file;
+    }
+    std::string msg = "Cannot find module '" + resolved.path() +
+        "' imported from " + base.ToFilePath();
+    node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
     return Nothing<URL>();
   }
-  if (!ShouldBeTreatedAsRelativeOrAbsolutePath(pjson.main)) {
-    return Resolve(env, "./" + pjson.main, search, IgnoreMain);
+
+  const std::string& path = resolved.ToFilePath();
+  if (CheckDescriptorAtPath(path) != FILE) {
+    std::string msg = "Cannot find module '" + path +
+        "' imported from " + base.ToFilePath();
+    node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
+    return Nothing<URL>();
   }
-  return Resolve(env, pjson.main, search, IgnoreMain);
+
+  return Just(resolved);
 }
 
-Maybe<URL> ResolveModule(Environment* env,
-                         const std::string& specifier,
-                         const URL& base) {
-  URL parent(".", base);
-  URL dir("");
-  do {
-    dir = parent;
-    Maybe<URL> check =
-        Resolve(env, "./node_modules/" + specifier, dir, CheckMain);
-    if (!check.IsNothing()) {
-      const size_t limit = specifier.find('/');
-      const size_t spec_len =
-          limit == std::string::npos ? specifier.length() :
-                                       limit + 1;
-      std::string chroot =
-          dir.path() + "node_modules/" + specifier.substr(0, spec_len);
-      if (check.FromJust().path().substr(0, chroot.length()) != chroot) {
-        return Nothing<URL>();
+Maybe<URL> PackageMainResolve(Environment* env,
+                              const URL& pjson_url,
+                              const PackageConfig& pcfg,
+                              const URL& base) {
+  if (pcfg.exists == Exists::Yes) {
+    if (pcfg.has_main == HasMain::Yes) {
+      URL resolved(pcfg.main, pjson_url);
+      const std::string& path = resolved.ToFilePath();
+      if (CheckDescriptorAtPath(path) == FILE) {
+        return Just(resolved);
+      }
+    }
+    if (env->options()->es_module_specifier_resolution == "node") {
+      if (pcfg.has_main == HasMain::Yes) {
+        return FinalizeResolution(env, URL(pcfg.main, pjson_url), base);
+      } else {
+        return FinalizeResolution(env, URL("index", pjson_url), base);
+      }
+    }
+    if (pcfg.type != PackageType::Module) {
+      Maybe<URL> resolved = LegacyMainResolve(pjson_url, pcfg);
+      if (!resolved.IsNothing()) {
+        return resolved;
       }
-      return check;
-    } else {
-      // TODO(bmeck) PREVENT FALLTHROUGH
     }
-    parent = URL("..", &dir);
-  } while (parent.path() != dir.path());
+  }
+  std::string msg = "Cannot find main entry point for '" +
+      URL(".", pjson_url).ToFilePath() + "' imported from " +
+      base.ToFilePath();
+  node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
   return Nothing<URL>();
 }
 
-Maybe<URL> ResolveDirectory(Environment* env,
-                            const URL& search,
-                            PackageMainCheck check_pjson_main) {
-  if (check_pjson_main) {
-    Maybe<URL> main = ResolveMain(env, search);
-    if (!main.IsNothing())
-      return main;
+Maybe<URL> PackageResolve(Environment* env,
+                          const std::string& specifier,
+                          const URL& base) {
+  size_t sep_index = specifier.find('/');
+  if (specifier[0] == '@' && (sep_index == std::string::npos ||
+      specifier.length() == 0)) {
+    std::string msg = "Invalid package name '" + specifier +
+      "' imported from " + base.ToFilePath();
+    node::THROW_ERR_INVALID_MODULE_SPECIFIER(env, msg.c_str());
+    return Nothing<URL>();
+  }
+  bool scope = false;
+  if (specifier[0] == '@') {
+    scope = true;
+    sep_index = specifier.find('/', sep_index + 1);
   }
-  return ResolveIndex(search);
+  std::string pkg_name = specifier.substr(0,
+      sep_index == std::string::npos ? std::string::npos : sep_index);
+  std::string pkg_subpath;
+  if ((sep_index == std::string::npos ||
+      sep_index == specifier.length() - 1)) {
+    pkg_subpath = "";
+  } else {
+    pkg_subpath = "." + specifier.substr(sep_index);
+  }
+  URL pjson_url("./node_modules/" + pkg_name + "/package.json", &base);
+  std::string pjson_path = pjson_url.ToFilePath();
+  std::string last_path;
+  do {
+    DescriptorType check =
+        CheckDescriptorAtPath(pjson_path.substr(0, pjson_path.length() - 13));
+    if (check != DIRECTORY) {
+      last_path = pjson_path;
+      pjson_url = URL((scope ?
+          "../../../../node_modules/" : "../../../node_modules/") +
+          pkg_name + "/package.json", &pjson_url);
+      pjson_path = pjson_url.ToFilePath();
+      continue;
+    }
+
+    // Package match.
+    Maybe<const PackageConfig*> pcfg = GetPackageConfig(env, pjson_path, base);
+    // Invalid package configuration error.
+    if (pcfg.IsNothing()) return Nothing<URL>();
+    if (!pkg_subpath.length()) {
+      return PackageMainResolve(env, pjson_url, *pcfg.FromJust(), base);
+    } else {
+      return FinalizeResolution(env, URL(pkg_subpath, pjson_url), base);
+    }
+    CHECK(false);
+    // Cross-platform root check.
+  } while (pjson_path.length() != last_path.length());
+
+  std::string msg = "Cannot find package '" + pkg_name +
+      "' imported from " + base.ToFilePath();
+  node::THROW_ERR_MODULE_NOT_FOUND(env, msg.c_str());
+  return Nothing<URL>();
 }
 
 }  // anonymous namespace
 
 Maybe<URL> Resolve(Environment* env,
                    const std::string& specifier,
-                   const URL& base,
-                   PackageMainCheck check_pjson_main) {
-  URL pure_url(specifier);
-  if (!(pure_url.flags() & URL_FLAGS_FAILED)) {
-    // just check existence, without altering
-    Maybe<uv_file> check = CheckFile(pure_url.ToFilePath());
-    if (check.IsNothing()) {
-      return Nothing<URL>();
-    }
-    return Just(pure_url);
-  }
-  if (specifier.length() == 0) {
-    return Nothing<URL>();
-  }
+                   const URL& base) {
+  // Order swapped from spec for minor perf gain.
+  // Ok since relative URLs cannot parse as URLs.
+  URL resolved;
   if (ShouldBeTreatedAsRelativeOrAbsolutePath(specifier)) {
-    URL resolved(specifier, base);
-    Maybe<URL> file = ResolveExtensions<TRY_EXACT_NAME>(resolved);
-    if (!file.IsNothing())
-      return file;
-    if (specifier.back() != '/') {
-      resolved = URL(specifier + "/", base);
-    }
-    return ResolveDirectory(env, resolved, check_pjson_main);
+    resolved = URL(specifier, base);
   } else {
-    return ResolveModule(env, specifier, base);
+    URL pure_url(specifier);
+    if (!(pure_url.flags() & URL_FLAGS_FAILED)) {
+      resolved = pure_url;
+    } else {
+      return PackageResolve(env, specifier, base);
+    }
   }
+  return FinalizeResolution(env, resolved, base);
 }
 
 void ModuleWrap::Resolve(const FunctionCallbackInfo<Value>& args) {
@@ -705,15 +897,40 @@ void ModuleWrap::Resolve(const FunctionCallbackInfo<Value>& args) {
         env, "second argument is not a URL string");
   }
 
-  Maybe<URL> result = node::loader::Resolve(env, specifier_std, url);
-  if (result.IsNothing() || (result.FromJust().flags() & URL_FLAGS_FAILED)) {
-    std::string msg = "Cannot find module " + specifier_std;
-    return node::THROW_ERR_MISSING_MODULE(env, msg.c_str());
+  Maybe<URL> result =
+      node::loader::Resolve(env,
+                            specifier_std,
+                            url);
+  if (result.IsNothing()) {
+    return;
+  }
+
+  URL resolution = result.FromJust();
+  CHECK(!(resolution.flags() & URL_FLAGS_FAILED));
+
+  Local<Value> resolution_obj;
+  if (resolution.ToObject(env).ToLocal(&resolution_obj))
+    args.GetReturnValue().Set(resolution_obj);
+}
+
+void ModuleWrap::GetPackageType(const FunctionCallbackInfo<Value>& args) {
+  Environment* env = Environment::GetCurrent(args);
+
+  // module.getPackageType(url)
+  CHECK_EQ(args.Length(), 1);
+
+  CHECK(args[0]->IsString());
+  Utf8Value url_utf8(env->isolate(), args[0]);
+  URL url(*url_utf8, url_utf8.length());
+
+  PackageType pkg_type = PackageType::None;
+  Maybe<const PackageConfig*> pcfg =
+      GetPackageScopeConfig(env, url, url);
+  if (!pcfg.IsNothing()) {
+    pkg_type = pcfg.FromJust()->type;
   }
 
-  MaybeLocal<Value> obj = result.FromJust().ToObject(env);
-  if (!obj.IsEmpty())
-    args.GetReturnValue().Set(obj.ToLocalChecked());
+  args.GetReturnValue().Set(Integer::New(env->isolate(), pkg_type));
 }
 
 static MaybeLocal<Promise> ImportModuleDynamically(
@@ -849,6 +1066,7 @@ void ModuleWrap::Initialize(Local<Object> target,
   target->Set(env->context(), FIXED_ONE_BYTE_STRING(isolate, "ModuleWrap"),
               tpl->GetFunction(context).ToLocalChecked()).FromJust();
   env->SetMethod(target, "resolve", Resolve);
+  env->SetMethod(target, "getPackageType", GetPackageType);
   env->SetMethod(target,
                  "setImportModuleDynamicallyCallback",
                  SetImportModuleDynamicallyCallback);
diff --git a/src/module_wrap.h b/src/module_wrap.h
index dc34685fed..6b7025f8a9 100644
--- a/src/module_wrap.h
+++ b/src/module_wrap.h
@@ -12,11 +12,6 @@
 namespace node {
 namespace loader {
 
-enum PackageMainCheck : bool {
-    CheckMain = true,
-    IgnoreMain = false
-};
-
 enum ScriptType : int {
   kScript,
   kModule,
@@ -29,11 +24,6 @@ enum HostDefinedOptions : int {
   kLength = 10,
 };
 
-v8::Maybe<url::URL> Resolve(Environment* env,
-                            const std::string& specifier,
-                            const url::URL& base,
-                            PackageMainCheck read_pkg_json = CheckMain);
-
 class ModuleWrap : public BaseObject {
  public:
   static const std::string EXTENSIONS[];
@@ -75,6 +65,7 @@ class ModuleWrap : public BaseObject {
       const v8::FunctionCallbackInfo<v8::Value>& args);
 
   static void Resolve(const v8::FunctionCallbackInfo<v8::Value>& args);
+  static void GetPackageType(const v8::FunctionCallbackInfo<v8::Value>& args);
   static void SetImportModuleDynamicallyCallback(
       const v8::FunctionCallbackInfo<v8::Value>& args);
   static void SetInitializeImportMetaObjectCallback(
diff --git a/src/node_errors.h b/src/node_errors.h
index 835794b178..9d3f2ead71 100644
--- a/src/node_errors.h
+++ b/src/node_errors.h
@@ -45,12 +45,14 @@ void FatalException(v8::Isolate* isolate,
   V(ERR_CONSTRUCT_CALL_REQUIRED, Error)                                      \
   V(ERR_INVALID_ARG_VALUE, TypeError)                                        \
   V(ERR_INVALID_ARG_TYPE, TypeError)                                         \
+  V(ERR_INVALID_MODULE_SPECIFIER, TypeError)                                 \
+  V(ERR_INVALID_PACKAGE_CONFIG, SyntaxError)                                 \
   V(ERR_INVALID_TRANSFER_OBJECT, TypeError)                                  \
   V(ERR_MEMORY_ALLOCATION_FAILED, Error)                                     \
   V(ERR_MISSING_ARGS, TypeError)                                             \
   V(ERR_MISSING_MESSAGE_PORT_IN_TRANSFER_LIST, TypeError)                    \
-  V(ERR_MISSING_MODULE, Error)                                               \
   V(ERR_MISSING_PLATFORM_FOR_WORKER, Error)                                  \
+  V(ERR_MODULE_NOT_FOUND, Error)                                             \
   V(ERR_OUT_OF_RANGE, RangeError)                                            \
   V(ERR_SCRIPT_EXECUTION_INTERRUPTED, Error)                                 \
   V(ERR_SCRIPT_EXECUTION_TIMEOUT, Error)                                     \
diff --git a/src/node_options.cc b/src/node_options.cc
index 5687fb327b..bd20b6385d 100644
--- a/src/node_options.cc
+++ b/src/node_options.cc
@@ -107,6 +107,32 @@ void EnvironmentOptions::CheckOptions(std::vector<std::string>* errors) {
     errors->push_back("--loader requires --experimental-modules be enabled");
   }
 
+  if (!module_type.empty()) {
+    if (!experimental_modules) {
+      errors->push_back("--entry-type requires "
+                        "--experimental-modules to be enabled");
+    }
+    if (module_type != "commonjs" && module_type != "module") {
+      errors->push_back("--entry-type must \"module\" or \"commonjs\"");
+    }
+  }
+
+  if (experimental_json_modules && !experimental_modules) {
+    errors->push_back("--experimental-json-modules requires "
+                      "--experimental-modules be enabled");
+  }
+
+  if (!es_module_specifier_resolution.empty()) {
+    if (!experimental_modules) {
+      errors->push_back("--es-module-specifier-resolution requires "
+                        "--experimental-modules be enabled");
+    }
+    if (es_module_specifier_resolution != "node" &&
+        es_module_specifier_resolution != "explicit") {
+      errors->push_back("invalid value for --es-module-specifier-resolution");
+    }
+  }
+
   if (syntax_check_only && has_eval_string) {
     errors->push_back("either --check or --eval can be used, not both");
   }
@@ -214,6 +240,10 @@ DebugOptionsParser::DebugOptionsParser() {
 }
 
 EnvironmentOptionsParser::EnvironmentOptionsParser() {
+  AddOption("--experimental-json-modules",
+            "experimental JSON interop support for the ES Module loader",
+            &EnvironmentOptions::experimental_json_modules,
+            kAllowedInEnvironment);
   AddOption("--experimental-modules",
             "experimental ES Module support and caching modules",
             &EnvironmentOptions::experimental_modules,
@@ -253,6 +283,11 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "custom loader",
             &EnvironmentOptions::userland_loader,
             kAllowedInEnvironment);
+  AddOption("--es-module-specifier-resolution",
+            "Select extension resolution algorithm for es modules; "
+            "either 'explicit' (default) or 'node'",
+            &EnvironmentOptions::es_module_specifier_resolution,
+            kAllowedInEnvironment);
   AddOption("--no-deprecation",
             "silence deprecation warnings",
             &EnvironmentOptions::no_deprecation,
@@ -271,10 +306,12 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             kAllowedInEnvironment);
   AddOption("--preserve-symlinks",
             "preserve symbolic links when resolving",
-            &EnvironmentOptions::preserve_symlinks);
+            &EnvironmentOptions::preserve_symlinks,
+            kAllowedInEnvironment);
   AddOption("--preserve-symlinks-main",
             "preserve symbolic links when resolving the main module",
-            &EnvironmentOptions::preserve_symlinks_main);
+            &EnvironmentOptions::preserve_symlinks_main,
+            kAllowedInEnvironment);
   AddOption("--prof-process",
             "process V8 profiler output generated using --prof",
             &EnvironmentOptions::prof_process);
@@ -301,6 +338,10 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
             "show stack traces on process warnings",
             &EnvironmentOptions::trace_warnings,
             kAllowedInEnvironment);
+  AddOption("--entry-type",
+            "set module type name of the entry point",
+            &EnvironmentOptions::module_type,
+            kAllowedInEnvironment);
 
   AddOption("--check",
             "syntax check script without executing",
diff --git a/src/node_options.h b/src/node_options.h
index bcd6d2457d..e07ee7fb35 100644
--- a/src/node_options.h
+++ b/src/node_options.h
@@ -91,7 +91,10 @@ class DebugOptions : public Options {
 class EnvironmentOptions : public Options {
  public:
   bool abort_on_uncaught_exception = false;
+  bool experimental_json_modules = false;
   bool experimental_modules = false;
+  std::string es_module_specifier_resolution;
+  std::string module_type;
   std::string experimental_policy;
   bool experimental_repl_await = false;
   bool experimental_vm_modules = false;
diff --git a/test/addons/hello-world-esm/binding.cc b/test/addons/hello-world-esm/binding.cc
deleted file mode 100644
index 02eecec099..0000000000
--- a/test/addons/hello-world-esm/binding.cc
+++ /dev/null
@@ -1,14 +0,0 @@
-#include <node.h>
-#include <v8.h>
-
-void Method(const v8::FunctionCallbackInfo<v8::Value>& args) {
-  v8::Isolate* isolate = args.GetIsolate();
-  args.GetReturnValue().Set(v8::String::NewFromUtf8(
-        isolate, "world", v8::NewStringType::kNormal).ToLocalChecked());
-}
-
-void init(v8::Local<v8::Object> exports) {
-  NODE_SET_METHOD(exports, "hello", Method);
-}
-
-NODE_MODULE(NODE_GYP_MODULE_NAME, init)
diff --git a/test/addons/hello-world-esm/binding.gyp b/test/addons/hello-world-esm/binding.gyp
deleted file mode 100644
index 55fbe7050f..0000000000
--- a/test/addons/hello-world-esm/binding.gyp
+++ /dev/null
@@ -1,9 +0,0 @@
-{
-  'targets': [
-    {
-      'target_name': 'binding',
-      'sources': [ 'binding.cc' ],
-      'includes': ['../common.gypi'],
-    }
-  ]
-}
diff --git a/test/addons/hello-world-esm/test.js b/test/addons/hello-world-esm/test.js
deleted file mode 100644
index d0faf65540..0000000000
--- a/test/addons/hello-world-esm/test.js
+++ /dev/null
@@ -1,20 +0,0 @@
-'use strict';
-const common = require('../../common');
-
-const assert = require('assert');
-const { spawnSync } = require('child_process');
-const { copyFileSync } = require('fs');
-const { join } = require('path');
-
-const buildDir = join(__dirname, 'build');
-
-copyFileSync(join(buildDir, common.buildType, 'binding.node'),
-             join(buildDir, 'binding.node'));
-
-const result = spawnSync(process.execPath,
-                         ['--experimental-modules', `${__dirname}/test.mjs`]);
-
-assert.ifError(result.error);
-// TODO: Uncomment this once ESM is no longer experimental.
-// assert.strictEqual(result.stderr.toString().trim(), '');
-assert.strictEqual(result.stdout.toString().trim(), 'binding.hello() = world');
diff --git a/test/addons/hello-world-esm/test.mjs b/test/addons/hello-world-esm/test.mjs
deleted file mode 100644
index d98de5bf87..0000000000
--- a/test/addons/hello-world-esm/test.mjs
+++ /dev/null
@@ -1,6 +0,0 @@
-/* eslint-disable node-core/required-modules */
-
-import assert from 'assert';
-import binding from './build/binding.node';
-assert.strictEqual(binding.hello(), 'world');
-console.log('binding.hello() =', binding.hello());
diff --git a/test/common/index.mjs b/test/common/index.mjs
index de9119f37e..41592098eb 100644
--- a/test/common/index.mjs
+++ b/test/common/index.mjs
@@ -1,6 +1,15 @@
 // Flags: --experimental-modules
 /* eslint-disable node-core/required-modules */
-import common from './index.js';
+
+import { createRequireFromPath } from 'module';
+import { fileURLToPath as toPath } from 'url';
+
+function createRequire(metaUrl) {
+  return createRequireFromPath(toPath(metaUrl));
+}
+
+const require = createRequire(import.meta.url);
+const common = require('./index.js');
 
 const {
   isMainThread,
@@ -91,5 +100,6 @@ export {
   getBufferSources,
   disableCrashOnUnhandledRejection,
   getTTYfd,
-  runWithInvalidFD
+  runWithInvalidFD,
+  createRequire
 };
diff --git a/test/es-module/test-esm-basic-imports.mjs b/test/es-module/test-esm-basic-imports.mjs
index 78a4106f94..d9bb22be0a 100644
--- a/test/es-module/test-esm-basic-imports.mjs
+++ b/test/es-module/test-esm-basic-imports.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
 import okShebang from './test-esm-shebang.mjs';
diff --git a/test/es-module/test-esm-cyclic-dynamic-import.mjs b/test/es-module/test-esm-cyclic-dynamic-import.mjs
index c8dfff919c..a207efc73e 100644
--- a/test/es-module/test-esm-cyclic-dynamic-import.mjs
+++ b/test/es-module/test-esm-cyclic-dynamic-import.mjs
@@ -1,3 +1,4 @@
 // Flags: --experimental-modules
-import '../common';
-import('./test-esm-cyclic-dynamic-import');
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import('./test-esm-cyclic-dynamic-import.mjs');
diff --git a/test/es-module/test-esm-double-encoding.mjs b/test/es-module/test-esm-double-encoding.mjs
index c81d0530d3..9366d4bd6b 100644
--- a/test/es-module/test-esm-double-encoding.mjs
+++ b/test/es-module/test-esm-double-encoding.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 
 // Assert we can import files with `%` in their pathname.
 
-import '../fixtures/es-modules/test-esm-double-encoding-native%2520.js';
+import '../fixtures/es-modules/test-esm-double-encoding-native%2520.mjs';
diff --git a/test/es-module/test-esm-dynamic-import.js b/test/es-module/test-esm-dynamic-import.js
index b271d43c80..ca9c99007b 100644
--- a/test/es-module/test-esm-dynamic-import.js
+++ b/test/es-module/test-esm-dynamic-import.js
@@ -1,4 +1,5 @@
 // Flags: --experimental-modules
+
 'use strict';
 const common = require('../common');
 const assert = require('assert');
@@ -17,7 +18,7 @@ function expectErrorProperty(result, propertyKey, value) {
 }
 
 function expectMissingModuleError(result) {
-  expectErrorProperty(result, 'code', 'MODULE_NOT_FOUND');
+  expectErrorProperty(result, 'code', 'ERR_MODULE_NOT_FOUND');
 }
 
 function expectOkNamespace(result) {
diff --git a/test/es-module/test-esm-encoded-path.mjs b/test/es-module/test-esm-encoded-path.mjs
index 365a425afa..2cabfdacff 100644
--- a/test/es-module/test-esm-encoded-path.mjs
+++ b/test/es-module/test-esm-encoded-path.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
 // ./test-esm-ok.mjs
 import ok from '../fixtures/es-modules/test-%65%73%6d-ok.mjs';
diff --git a/test/es-module/test-esm-error-cache.js b/test/es-module/test-esm-error-cache.js
index 98244615ef..79f76357ec 100644
--- a/test/es-module/test-esm-error-cache.js
+++ b/test/es-module/test-esm-error-cache.js
@@ -1,11 +1,11 @@
-'use strict';
-
 // Flags: --experimental-modules
 
+'use strict';
+
 require('../common');
 const assert = require('assert');
 
-const file = '../fixtures/syntax/bad_syntax.js';
+const file = '../fixtures/syntax/bad_syntax.mjs';
 
 let error;
 (async () => {
diff --git a/test/es-module/test-esm-forbidden-globals.mjs b/test/es-module/test-esm-forbidden-globals.mjs
index 4e777412a3..cf110ff290 100644
--- a/test/es-module/test-esm-forbidden-globals.mjs
+++ b/test/es-module/test-esm-forbidden-globals.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 
 // eslint-disable-next-line no-undef
 if (typeof arguments !== 'undefined') {
diff --git a/test/es-module/test-esm-import-meta.mjs b/test/es-module/test-esm-import-meta.mjs
index c17e0e20d4..4c34b337fb 100644
--- a/test/es-module/test-esm-import-meta.mjs
+++ b/test/es-module/test-esm-import-meta.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules
+/* eslint-disable node-core/required-modules */
 
-import '../common';
+import '../common/index.mjs';
 import assert from 'assert';
 
 assert.strictEqual(Object.getPrototypeOf(import.meta), null);
diff --git a/test/es-module/test-esm-json-cache.mjs b/test/es-module/test-esm-json-cache.mjs
new file mode 100644
index 0000000000..ecd27c5488
--- /dev/null
+++ b/test/es-module/test-esm-json-cache.mjs
@@ -0,0 +1,26 @@
+// Flags: --experimental-modules --experimental-json-modules
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+
+import { strictEqual, deepStrictEqual } from 'assert';
+
+import { createRequireFromPath as createRequire } from 'module';
+import { fileURLToPath as fromURL } from 'url';
+
+import mod from '../fixtures/es-modules/json-cache/mod.cjs';
+import another from '../fixtures/es-modules/json-cache/another.cjs';
+import test from '../fixtures/es-modules/json-cache/test.json';
+
+const require = createRequire(fromURL(import.meta.url));
+
+const modCjs = require('../fixtures/es-modules/json-cache/mod.cjs');
+const anotherCjs = require('../fixtures/es-modules/json-cache/another.cjs');
+const testCjs = require('../fixtures/es-modules/json-cache/test.json');
+
+strictEqual(mod.one, 1);
+strictEqual(another.one, 'zalgo');
+strictEqual(test.one, 'it comes');
+
+deepStrictEqual(mod, modCjs);
+deepStrictEqual(another, anotherCjs);
+deepStrictEqual(test, testCjs);
diff --git a/test/es-module/test-esm-json.mjs b/test/es-module/test-esm-json.mjs
index a7146d19a9..b140d031ca 100644
--- a/test/es-module/test-esm-json.mjs
+++ b/test/es-module/test-esm-json.mjs
@@ -1,8 +1,9 @@
-// Flags: --experimental-modules
-import '../common';
-import assert from 'assert';
-import ok from '../fixtures/es-modules/test-esm-ok.mjs';
-import json from '../fixtures/es-modules/json.json';
+// Flags: --experimental-modules --experimental-json-modules
+/* eslint-disable node-core/required-modules */
 
-assert(ok);
-assert.strictEqual(json.val, 42);
+import '../common/index.mjs';
+import { strictEqual } from 'assert';
+
+import secret from '../fixtures/experimental.json';
+
+strictEqual(secret.ofLife, 42);
diff --git a/test/es-module/test-esm-live-binding.mjs b/test/es-module/test-esm-live-binding.mjs
index d151e004df..880a6c389b 100644
--- a/test/es-module/test-esm-live-binding.mjs
+++ b/test/es-module/test-esm-live-binding.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules
+/* eslint-disable node-core/required-modules */
 
-import '../common';
+import '../common/index.mjs';
 import assert from 'assert';
 
 import fs, { readFile, readFileSync } from 'fs';
diff --git a/test/es-module/test-esm-loader-invalid-format.mjs b/test/es-module/test-esm-loader-invalid-format.mjs
index f8714d4aa1..c3f3a87407 100644
--- a/test/es-module/test-esm-loader-invalid-format.mjs
+++ b/test/es-module/test-esm-loader-invalid-format.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-format.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
+import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 
 import('../fixtures/es-modules/test-esm-ok.mjs')
diff --git a/test/es-module/test-esm-loader-invalid-url.mjs b/test/es-module/test-esm-loader-invalid-url.mjs
index 43971a2e6e..9cf17b2478 100644
--- a/test/es-module/test-esm-loader-invalid-url.mjs
+++ b/test/es-module/test-esm-loader-invalid-url.mjs
@@ -1,5 +1,7 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-invalid-url.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
+
+import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 
 import('../fixtures/es-modules/test-esm-ok.mjs')
diff --git a/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs b/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
index f2b37f7e8a..ab2da7adce 100644
--- a/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
+++ b/test/es-module/test-esm-loader-missing-dynamic-instantiate-hook.mjs
@@ -1,6 +1,7 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/missing-dynamic-instantiate-hook.mjs
+/* eslint-disable node-core/required-modules */
 
-import { expectsError } from '../common';
+import { expectsError } from '../common/index.mjs';
 
 import('test').catch(expectsError({
   code: 'ERR_MISSING_DYNAMIC_INSTANTIATE_HOOK',
diff --git a/test/es-module/test-esm-loader-modulemap.js b/test/es-module/test-esm-loader-modulemap.js
index 946d54ffaa..5493c6c47c 100644
--- a/test/es-module/test-esm-loader-modulemap.js
+++ b/test/es-module/test-esm-loader-modulemap.js
@@ -7,7 +7,7 @@
 const common = require('../common');
 
 const { URL } = require('url');
-const Loader = require('internal/modules/esm/loader');
+const { Loader } = require('internal/modules/esm/loader');
 const ModuleMap = require('internal/modules/esm/module_map');
 const ModuleJob = require('internal/modules/esm/module_job');
 const createDynamicModule = require(
diff --git a/test/es-module/test-esm-loader-search.js b/test/es-module/test-esm-loader-search.js
index 0ca8990cb7..b5e0d8d656 100644
--- a/test/es-module/test-esm-loader-search.js
+++ b/test/es-module/test-esm-loader-search.js
@@ -5,13 +5,13 @@
 
 const common = require('../common');
 
-const { search } = require('internal/modules/esm/default_resolve');
+const resolve = require('internal/modules/esm/default_resolve');
 
 common.expectsError(
-  () => search('target', undefined),
+  () => resolve('target', undefined),
   {
-    code: 'ERR_MISSING_MODULE',
+    code: 'ERR_MODULE_NOT_FOUND',
     type: Error,
-    message: 'Cannot find module target'
+    message: /Cannot find package 'target'/
   }
 );
diff --git a/test/es-module/test-esm-main-lookup.mjs b/test/es-module/test-esm-main-lookup.mjs
index ca313a1d26..19c025beab 100644
--- a/test/es-module/test-esm-main-lookup.mjs
+++ b/test/es-module/test-esm-main-lookup.mjs
@@ -1,6 +1,26 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
-import main from '../fixtures/es-modules/pjson-main';
 
-assert.strictEqual(main, 'main');
+async function main() {
+  let mod;
+  try {
+    mod = await import('../fixtures/es-modules/pjson-main');
+  } catch (e) {
+    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
+  }
+
+  assert.strictEqual(mod, undefined);
+
+  try {
+    mod = await import('../fixtures/es-modules/pjson-main/main.mjs');
+  } catch (e) {
+    console.log(e);
+    assert.fail();
+  }
+
+  assert.strictEqual(mod.main, 'main');
+}
+
+main();
diff --git a/test/es-module/test-esm-named-exports.mjs b/test/es-module/test-esm-named-exports.mjs
index 3aae9230de..e235f598cb 100644
--- a/test/es-module/test-esm-named-exports.mjs
+++ b/test/es-module/test-esm-named-exports.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/builtin-named-exports-loader.mjs
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import { readFile } from 'fs';
 import assert from 'assert';
 import ok from '../fixtures/es-modules/test-esm-ok.mjs';
diff --git a/test/es-module/test-esm-namespace.mjs b/test/es-module/test-esm-namespace.mjs
index da1286d0f4..38b7ef12d5 100644
--- a/test/es-module/test-esm-namespace.mjs
+++ b/test/es-module/test-esm-namespace.mjs
@@ -1,5 +1,7 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+
+import '../common/index.mjs';
 import * as fs from 'fs';
 import assert from 'assert';
 import Module from 'module';
diff --git a/test/es-module/test-esm-no-extension.js b/test/es-module/test-esm-no-extension.js
new file mode 100644
index 0000000000..3e9ffb2bbc
--- /dev/null
+++ b/test/es-module/test-esm-no-extension.js
@@ -0,0 +1,35 @@
+'use strict';
+
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const { spawn } = require('child_process');
+const assert = require('assert');
+
+const entry = fixtures.path('/es-modules/noext-esm');
+
+// Run a module that does not have extension
+// This is to ensure the --entry-type works as expected
+
+const child = spawn(process.execPath, [
+  '--experimental-modules',
+  '--entry-type=module',
+  entry
+]);
+
+let stderr = '';
+child.stderr.setEncoding('utf8');
+child.stderr.on('data', (data) => {
+  stderr += data;
+});
+let stdout = '';
+child.stdout.setEncoding('utf8');
+child.stdout.on('data', (data) => {
+  stdout += data;
+});
+child.on('close', common.mustCall((code, signal) => {
+  assert.strictEqual(code, 0);
+  assert.strictEqual(signal, null);
+  assert.strictEqual(stdout, 'executed\n');
+  assert.strictEqual(stderr, `(node:${child.pid}) ` +
+      'ExperimentalWarning: The ESM module loader is experimental.\n');
+}));
diff --git a/test/es-module/test-esm-preserve-symlinks-not-found.mjs b/test/es-module/test-esm-preserve-symlinks-not-found.mjs
index 5119957bae..b5be2d7e63 100644
--- a/test/es-module/test-esm-preserve-symlinks-not-found.mjs
+++ b/test/es-module/test-esm-preserve-symlinks-not-found.mjs
@@ -1,3 +1,3 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/not-found-assert-loader.mjs
 /* eslint-disable node-core/required-modules */
-import './not-found';
+import './not-found.mjs';
diff --git a/test/es-module/test-esm-process.mjs b/test/es-module/test-esm-process.mjs
index ea9b4b4936..3a23573d33 100644
--- a/test/es-module/test-esm-process.mjs
+++ b/test/es-module/test-esm-process.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 import assert from 'assert';
 import process from 'process';
 
diff --git a/test/es-module/test-esm-require-cache.mjs b/test/es-module/test-esm-require-cache.mjs
index ff32cde36f..09030e0578 100644
--- a/test/es-module/test-esm-require-cache.mjs
+++ b/test/es-module/test-esm-require-cache.mjs
@@ -1,7 +1,12 @@
 // Flags: --experimental-modules
-import '../common';
-import '../fixtures/es-module-require-cache/preload.js';
-import '../fixtures/es-module-require-cache/counter.js';
+/* eslint-disable node-core/required-modules */
+import { createRequire } from '../common/index.mjs';
 import assert from 'assert';
+//
+const require = createRequire(import.meta.url);
+
+require('../fixtures/es-module-require-cache/preload.js');
+require('../fixtures/es-module-require-cache/counter.js');
+
 assert.strictEqual(global.counter, 1);
 delete global.counter;
diff --git a/test/es-module/test-esm-shared-loader-dep.mjs b/test/es-module/test-esm-shared-loader-dep.mjs
index 5c274d835c..b8953ab1ec 100644
--- a/test/es-module/test-esm-shared-loader-dep.mjs
+++ b/test/es-module/test-esm-shared-loader-dep.mjs
@@ -1,7 +1,11 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-shared-dep.mjs
-import '../common';
+/* eslint-disable node-core/required-modules */
+import { createRequire } from '../common/index.mjs';
+
 import assert from 'assert';
 import '../fixtures/es-modules/test-esm-ok.mjs';
-import dep from '../fixtures/es-module-loaders/loader-dep.js';
 
-assert.strictEqual(dep.format, 'esm');
+const require = createRequire(import.meta.url);
+const dep = require('../fixtures/es-module-loaders/loader-dep.js');
+
+assert.strictEqual(dep.format, 'module');
diff --git a/test/es-module/test-esm-shebang.mjs b/test/es-module/test-esm-shebang.mjs
index d5faace479..486e04dade 100644
--- a/test/es-module/test-esm-shebang.mjs
+++ b/test/es-module/test-esm-shebang.mjs
@@ -1,6 +1,7 @@
 #! }]) // isn't js
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
 
 const isJs = true;
 export default isJs;
diff --git a/test/es-module/test-esm-snapshot.mjs b/test/es-module/test-esm-snapshot.mjs
index 3d4b44bbdd..3997e24ed7 100644
--- a/test/es-module/test-esm-snapshot.mjs
+++ b/test/es-module/test-esm-snapshot.mjs
@@ -1,7 +1,8 @@
 // Flags: --experimental-modules
-import '../common';
-import '../fixtures/es-modules/esm-snapshot-mutator';
-import one from '../fixtures/es-modules/esm-snapshot';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import '../fixtures/es-modules/esm-snapshot-mutator.js';
+import one from '../fixtures/es-modules/esm-snapshot.js';
 import assert from 'assert';
 
 assert.strictEqual(one, 1);
diff --git a/test/es-module/test-esm-specifiers.mjs b/test/es-module/test-esm-specifiers.mjs
new file mode 100644
index 0000000000..0c5e1ac04a
--- /dev/null
+++ b/test/es-module/test-esm-specifiers.mjs
@@ -0,0 +1,35 @@
+// Flags: --experimental-modules --es-module-specifier-resolution=node
+import { mustNotCall } from '../common';
+import assert from 'assert';
+
+// commonJS index.js
+import commonjs from '../fixtures/es-module-specifiers/package-type-commonjs';
+// esm index.js
+import module from '../fixtures/es-module-specifiers/package-type-module';
+// Notice the trailing slash
+import success, { explicit, implicit, implicitModule, getImplicitCommonjs }
+  from '../fixtures/es-module-specifiers/';
+
+assert.strictEqual(commonjs, 'commonjs');
+assert.strictEqual(module, 'module');
+assert.strictEqual(success, 'success');
+assert.strictEqual(explicit, 'esm');
+assert.strictEqual(implicit, 'esm');
+assert.strictEqual(implicitModule, 'esm');
+
+async function main() {
+  try {
+    await import('../fixtures/es-module-specifiers/do-not-exist.js');
+  } catch (e) {
+    // Files that do not exist should throw
+    assert.strictEqual(e.name, 'Error');
+  }
+  try {
+    await getImplicitCommonjs();
+  } catch (e) {
+    // Legacy loader cannot resolve .mjs automatically from main
+    assert.strictEqual(e.name, 'Error');
+  }
+}
+
+main().catch(mustNotCall);
diff --git a/test/es-module/test-esm-symlink-main.js b/test/es-module/test-esm-symlink-main.js
index f7631ef2e5..871180f5cc 100644
--- a/test/es-module/test-esm-symlink-main.js
+++ b/test/es-module/test-esm-symlink-main.js
@@ -9,7 +9,7 @@ const fs = require('fs');
 tmpdir.refresh();
 
 const realPath = path.resolve(__dirname, '../fixtures/es-modules/symlink.mjs');
-const symlinkPath = path.resolve(tmpdir.path, 'symlink.js');
+const symlinkPath = path.resolve(tmpdir.path, 'symlink.mjs');
 
 try {
   fs.symlinkSync(realPath, symlinkPath);
diff --git a/test/es-module/test-esm-symlink-type.js b/test/es-module/test-esm-symlink-type.js
new file mode 100644
index 0000000000..6159ebecd1
--- /dev/null
+++ b/test/es-module/test-esm-symlink-type.js
@@ -0,0 +1,77 @@
+'use strict';
+const common = require('../common');
+const fixtures = require('../common/fixtures');
+const path = require('path');
+const assert = require('assert');
+const exec = require('child_process').execFile;
+const fs = require('fs');
+
+const tmpdir = require('../common/tmpdir');
+tmpdir.refresh();
+const tmpDir = tmpdir.path;
+
+// Check that running the symlink executes the target as the correct type
+const symlinks = [
+  {
+    source: 'extensionless-symlink-to-mjs-file',
+    target: fixtures.path('es-modules/mjs-file.mjs'),
+    prints: '.mjs file',
+    errorsWithPreserveSymlinksMain: false
+  }, {
+    source: 'extensionless-symlink-to-cjs-file',
+    target: fixtures.path('es-modules/cjs-file.cjs'),
+    prints: '.cjs file',
+    errorsWithPreserveSymlinksMain: false
+  }, {
+    source: 'extensionless-symlink-to-file-in-module-scope',
+    target: fixtures.path('es-modules/package-type-module/index.js'),
+    prints: 'package-type-module',
+    // The package scope of the symlinks' sources is commonjs, and this
+    // symlink's target is a .js file in a module scope, so when the scope
+    // is evaluated based on the source (commonjs) this esm file should error
+    errorsWithPreserveSymlinksMain: true
+  }, {
+    source: 'extensionless-symlink-to-file-in-explicit-commonjs-scope',
+    target: fixtures.path('es-modules/package-type-commonjs/index.js'),
+    prints: 'package-type-commonjs',
+    errorsWithPreserveSymlinksMain: false
+  }, {
+    source: 'extensionless-symlink-to-file-in-implicit-commonjs-scope',
+    target: fixtures.path('es-modules/package-without-type/index.js'),
+    prints: 'package-without-type',
+    errorsWithPreserveSymlinksMain: false
+  }
+];
+
+symlinks.forEach((symlink) => {
+  const mainPath = path.join(tmpDir, symlink.source);
+  fs.symlinkSync(symlink.target, mainPath);
+
+  const flags = [
+    '--experimental-modules',
+    '--experimental-modules --preserve-symlinks-main'
+  ];
+  flags.forEach((nodeOptions) => {
+    const opts = {
+      env: Object.assign({}, process.env, { NODE_OPTIONS: nodeOptions })
+    };
+    exec(process.execPath, [mainPath], opts, common.mustCall(
+      (err, stdout) => {
+        if (nodeOptions.includes('--preserve-symlinks-main')) {
+          if (symlink.errorsWithPreserveSymlinksMain &&
+              err.toString().includes('Error')) return;
+          else if (!symlink.errorsWithPreserveSymlinksMain &&
+                    stdout.includes(symlink.prints)) return;
+          assert.fail(`For ${JSON.stringify(symlink)}, ${
+            (symlink.errorsWithPreserveSymlinksMain) ?
+              'failed to error' : 'errored unexpectedly'
+          } with --preserve-symlinks-main`);
+        } else {
+          if (stdout.includes(symlink.prints)) return;
+          assert.fail(`For ${JSON.stringify(symlink)}, failed to find ` +
+            `${symlink.prints} in: <\n${stdout}\n>`);
+        }
+      }
+    ));
+  });
+});
diff --git a/test/es-module/test-esm-symlink.js b/test/es-module/test-esm-symlink.js
index 232925a52e..9b9eb98cd9 100644
--- a/test/es-module/test-esm-symlink.js
+++ b/test/es-module/test-esm-symlink.js
@@ -12,8 +12,8 @@ const tmpDir = tmpdir.path;
 
 const entry = path.join(tmpDir, 'entry.mjs');
 const real = path.join(tmpDir, 'index.mjs');
-const link_absolute_path = path.join(tmpDir, 'absolute');
-const link_relative_path = path.join(tmpDir, 'relative');
+const link_absolute_path = path.join(tmpDir, 'absolute.mjs');
+const link_relative_path = path.join(tmpDir, 'relative.mjs');
 const link_ignore_extension = path.join(tmpDir,
                                         'ignore_extension.json');
 const link_directory = path.join(tmpDir, 'directory');
@@ -22,15 +22,13 @@ fs.writeFileSync(real, 'export default [];');
 fs.writeFileSync(entry, `
 import assert from 'assert';
 import real from './index.mjs';
-import absolute from './absolute';
-import relative from './relative';
+import absolute from './absolute.mjs';
+import relative from './relative.mjs';
 import ignoreExtension from './ignore_extension.json';
-import directory from './directory';
 
 assert.strictEqual(absolute, real);
 assert.strictEqual(relative, real);
 assert.strictEqual(ignoreExtension, real);
-assert.strictEqual(directory, real);
 `);
 
 try {
diff --git a/test/es-module/test-esm-throw-undefined.mjs b/test/es-module/test-esm-throw-undefined.mjs
index 541127eee5..97e917da5e 100644
--- a/test/es-module/test-esm-throw-undefined.mjs
+++ b/test/es-module/test-esm-throw-undefined.mjs
@@ -1,11 +1,13 @@
 // Flags: --experimental-modules
-import '../common';
+/* eslint-disable node-core/required-modules */
+
+import '../common/index.mjs';
 import assert from 'assert';
 
 async function doTest() {
   await assert.rejects(
     async () => {
-      await import('../fixtures/es-module-loaders/throw-undefined');
+      await import('../fixtures/es-module-loaders/throw-undefined.mjs');
     },
     (e) => e === undefined
   );
diff --git a/test/es-module/test-esm-type-flag-errors.js b/test/es-module/test-esm-type-flag-errors.js
new file mode 100644
index 0000000000..612ada584d
--- /dev/null
+++ b/test/es-module/test-esm-type-flag-errors.js
@@ -0,0 +1,53 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const exec = require('child_process').execFile;
+
+const mjsFile = require.resolve('../fixtures/es-modules/mjs-file.mjs');
+const cjsFile = require.resolve('../fixtures/es-modules/cjs-file.cjs');
+const packageWithoutTypeMain =
+  require.resolve('../fixtures/es-modules/package-without-type/index.js');
+const packageTypeCommonJsMain =
+  require.resolve('../fixtures/es-modules/package-type-commonjs/index.js');
+const packageTypeModuleMain =
+  require.resolve('../fixtures/es-modules/package-type-module/index.js');
+
+// Check that running `node` without options works
+expect('', mjsFile, '.mjs file');
+expect('', cjsFile, '.cjs file');
+expect('', packageTypeModuleMain, 'package-type-module');
+expect('', packageTypeCommonJsMain, 'package-type-commonjs');
+expect('', packageWithoutTypeMain, 'package-without-type');
+
+// Check that running with --entry-type and no package.json "type" works
+expect('--entry-type=commonjs', packageWithoutTypeMain, 'package-without-type');
+expect('--entry-type=module', packageWithoutTypeMain, 'package-without-type');
+
+// Check that running with conflicting --entry-type flags throws errors
+expect('--entry-type=commonjs', mjsFile, 'ERR_ENTRY_TYPE_MISMATCH', true);
+expect('--entry-type=module', cjsFile, 'ERR_ENTRY_TYPE_MISMATCH', true);
+expect('--entry-type=commonjs', packageTypeModuleMain,
+       'ERR_ENTRY_TYPE_MISMATCH', true);
+expect('--entry-type=module', packageTypeCommonJsMain,
+       'ERR_ENTRY_TYPE_MISMATCH', true);
+
+function expect(opt = '', inputFile, want, wantsError = false) {
+  // TODO: Remove when --experimental-modules is unflagged
+  opt = `--experimental-modules ${opt}`;
+  const argv = [inputFile];
+  const opts = {
+    env: Object.assign({}, process.env, { NODE_OPTIONS: opt }),
+    maxBuffer: 1e6,
+  };
+  exec(process.execPath, argv, opts, common.mustCall((err, stdout, stderr) => {
+    if (wantsError) {
+      stdout = stderr;
+    } else {
+      assert.ifError(err);
+    }
+    if (stdout.includes(want)) return;
+
+    const o = JSON.stringify(opt);
+    assert.fail(`For ${o}, failed to find ${want} in: <\n${stdout}\n>`);
+  }));
+}
diff --git a/test/es-module/test-esm-type-flag.mjs b/test/es-module/test-esm-type-flag.mjs
new file mode 100644
index 0000000000..2f5d0b626a
--- /dev/null
+++ b/test/es-module/test-esm-type-flag.mjs
@@ -0,0 +1,11 @@
+// Flags: --experimental-modules --entry-type=module
+/* eslint-disable node-core/required-modules */
+import cjs from '../fixtures/baz.js';
+import '../common/index.mjs';
+import { message } from '../fixtures/es-modules/message.mjs';
+import assert from 'assert';
+
+// Assert we loaded esm dependency as ".js" in this mode
+assert.strictEqual(message, 'A message');
+// Assert we loaded CommonJS dependency
+assert.strictEqual(cjs, 'perhaps I work');
diff --git a/test/fixtures/es-module-loaders/example-loader.mjs b/test/fixtures/es-module-loaders/example-loader.mjs
index a7cf276d4a..d8e0ddcba3 100644
--- a/test/fixtures/es-module-loaders/example-loader.mjs
+++ b/test/fixtures/es-module-loaders/example-loader.mjs
@@ -29,6 +29,6 @@ export function resolve(specifier, parentModuleURL = baseURL /*, defaultResolve
   }
   return {
     url: resolved.href,
-    format: 'esm'
+    format: 'module'
   };
 }
diff --git a/test/fixtures/es-module-loaders/js-loader.mjs b/test/fixtures/es-module-loaders/js-loader.mjs
index 2ac959a464..4b8a0fc365 100644
--- a/test/fixtures/es-module-loaders/js-loader.mjs
+++ b/test/fixtures/es-module-loaders/js-loader.mjs
@@ -15,6 +15,6 @@ export function resolve (specifier, base = baseURL) {
   const url = new URL(specifier, base).href;
   return {
     url,
-    format: 'esm'
+    format: 'module'
   };
 }
diff --git a/test/fixtures/es-module-loaders/loader-dep.js b/test/fixtures/es-module-loaders/loader-dep.js
index cf821afec1..c8154ac5db 100644
--- a/test/fixtures/es-module-loaders/loader-dep.js
+++ b/test/fixtures/es-module-loaders/loader-dep.js
@@ -1 +1 @@
-exports.format = 'esm';
+exports.format = 'module';
diff --git a/test/fixtures/es-module-loaders/loader-invalid-url.mjs b/test/fixtures/es-module-loaders/loader-invalid-url.mjs
index 12efbb5021..f653155899 100644
--- a/test/fixtures/es-module-loaders/loader-invalid-url.mjs
+++ b/test/fixtures/es-module-loaders/loader-invalid-url.mjs
@@ -1,3 +1,4 @@
+/* eslint-disable node-core/required-modules */
 export async function resolve(specifier, parentModuleURL, defaultResolve) {
   if (parentModuleURL && specifier === '../fixtures/es-modules/test-esm-ok.mjs') {
     return {
diff --git a/test/fixtures/es-module-loaders/loader-shared-dep.mjs b/test/fixtures/es-module-loaders/loader-shared-dep.mjs
index 1a19e4c892..3acafcce1e 100644
--- a/test/fixtures/es-module-loaders/loader-shared-dep.mjs
+++ b/test/fixtures/es-module-loaders/loader-shared-dep.mjs
@@ -1,7 +1,11 @@
-import dep from './loader-dep.js';
 import assert from 'assert';
 
+import {createRequire} from '../../common/index.mjs';
+
+const require = createRequire(import.meta.url);
+const dep = require('./loader-dep.js');
+
 export function resolve(specifier, base, defaultResolve) {
-  assert.strictEqual(dep.format, 'esm');
+  assert.strictEqual(dep.format, 'module');
   return defaultResolve(specifier, base);
 }
diff --git a/test/fixtures/es-module-loaders/loader-with-dep.mjs b/test/fixtures/es-module-loaders/loader-with-dep.mjs
index 944e6e438c..5afd3b2e21 100644
--- a/test/fixtures/es-module-loaders/loader-with-dep.mjs
+++ b/test/fixtures/es-module-loaders/loader-with-dep.mjs
@@ -1,4 +1,8 @@
-import dep from './loader-dep.js';
+import {createRequire} from '../../common/index.mjs';
+
+const require = createRequire(import.meta.url);
+const dep = require('./loader-dep.js');
+
 export function resolve (specifier, base, defaultResolve) {
   return {
     url: defaultResolve(specifier, base).url,
diff --git a/test/fixtures/es-module-loaders/not-found-assert-loader.mjs b/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
index d15f294fe6..d3eebcd47e 100644
--- a/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
+++ b/test/fixtures/es-module-loaders/not-found-assert-loader.mjs
@@ -12,11 +12,11 @@ export async function resolve (specifier, base, defaultResolve) {
     await defaultResolve(specifier, base);
   }
   catch (e) {
-    assert.strictEqual(e.code, 'MODULE_NOT_FOUND');
+    assert.strictEqual(e.code, 'ERR_MODULE_NOT_FOUND');
     return {
       format: 'builtin',
       url: 'fs'
     };
   }
-  assert.fail(`Module resolution for ${specifier} should be throw MODULE_NOT_FOUND`);
+  assert.fail(`Module resolution for ${specifier} should be throw ERR_MODULE_NOT_FOUND`);
 }
diff --git a/test/fixtures/es-module-loaders/syntax-error-import.mjs b/test/fixtures/es-module-loaders/syntax-error-import.mjs
index 9cad68c7ce..3a6bc5effc 100644
--- a/test/fixtures/es-module-loaders/syntax-error-import.mjs
+++ b/test/fixtures/es-module-loaders/syntax-error-import.mjs
@@ -1 +1 @@
-import { foo, notfound } from './module-named-exports';
+import { foo, notfound } from './module-named-exports.mjs';
diff --git a/test/fixtures/es-module-loaders/throw-undefined.mjs b/test/fixtures/es-module-loaders/throw-undefined.mjs
index f062276767..0349ae112d 100644
--- a/test/fixtures/es-module-loaders/throw-undefined.mjs
+++ b/test/fixtures/es-module-loaders/throw-undefined.mjs
@@ -1,3 +1,4 @@
 'use strict';
+/* eslint-disable node-core/required-modules */
 
 throw undefined;
diff --git a/test/fixtures/es-module-specifiers/index.mjs b/test/fixtures/es-module-specifiers/index.mjs
new file mode 100644
index 0000000000..2be7048513
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/index.mjs
@@ -0,0 +1,10 @@
+import explicit from 'explicit-main';
+import implicit from 'implicit-main';
+import implicitModule from 'implicit-main-type-module';
+
+function getImplicitCommonjs () {
+  return import('implicit-main-type-commonjs');
+}
+
+export {explicit, implicit, implicitModule, getImplicitCommonjs};
+export default 'success';
diff --git a/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/explicit-main/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json b/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json
new file mode 100644
index 0000000000..e9457582ac
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/explicit-main/package.json
@@ -0,0 +1,3 @@
+{
+  "main": "entry.mjs"
+}
\ No newline at end of file
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json
new file mode 100644
index 0000000000..9093a7cc14
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-commonjs/package.json
@@ -0,0 +1,4 @@
+{
+  "main": "entry",
+  "type": "commonjs"
+}
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js
new file mode 100644
index 0000000000..5d7af588fd
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.js
@@ -0,0 +1 @@
+export default 'nope';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json
new file mode 100644
index 0000000000..5710280bad
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main-type-module/package.json
@@ -0,0 +1,4 @@
+{
+  "main": "entry",
+  "type": "module"
+}
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js
new file mode 100644
index 0000000000..b2825bd3c9
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.js
@@ -0,0 +1 @@
+module.exports = 'cjs';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs
new file mode 100644
index 0000000000..914e3a97d5
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/entry.mjs
@@ -0,0 +1 @@
+export default 'esm';
diff --git a/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json b/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json
new file mode 100644
index 0000000000..5c07cf41bb
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/node_modules/implicit-main/package.json
@@ -0,0 +1,3 @@
+{
+  "main": "entry"
+}
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/a.js b/test/fixtures/es-module-specifiers/package-type-commonjs/a.js
new file mode 100644
index 0000000000..2e7700bc63
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/a.js
@@ -0,0 +1 @@
+module.exports = 'a';
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs b/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs
new file mode 100644
index 0000000000..137b8ce642
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/b.mjs
@@ -0,0 +1 @@
+export const b = 'b';
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs b/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs
new file mode 100644
index 0000000000..2d5312952f
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/c.cjs
@@ -0,0 +1,5 @@
+module.exports = {
+  one: 1,
+  two: 2,
+  three: 3
+};
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs b/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs
new file mode 100644
index 0000000000..ef2b30b19b
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/index.mjs
@@ -0,0 +1,21 @@
+// js file that is common.js
+import a from './a.js';
+// ESM with named export
+import {b} from './b.mjs';
+// import 'c.cjs';
+import cjs from './c.cjs';
+// proves cross boundary fun bits
+import jsAsEsm from '../package-type-module/a.js';
+
+// named export from core
+import {strictEqual, deepStrictEqual} from 'assert';
+
+strictEqual(a, jsAsEsm);
+strictEqual(b, 'b');
+deepStrictEqual(cjs, {
+  one: 1,
+  two: 2,
+  three: 3
+});
+
+export default 'commonjs';
diff --git a/test/fixtures/es-module-specifiers/package-type-commonjs/package.json b/test/fixtures/es-module-specifiers/package-type-commonjs/package.json
new file mode 100644
index 0000000000..5bbefffbab
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-commonjs/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "commonjs"
+}
diff --git a/test/fixtures/es-module-specifiers/package-type-module/a.js b/test/fixtures/es-module-specifiers/package-type-module/a.js
new file mode 100644
index 0000000000..90bd54cd7f
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/a.js
@@ -0,0 +1 @@
+export default 'a'
diff --git a/test/fixtures/es-module-specifiers/package-type-module/b.mjs b/test/fixtures/es-module-specifiers/package-type-module/b.mjs
new file mode 100644
index 0000000000..137b8ce642
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/b.mjs
@@ -0,0 +1 @@
+export const b = 'b';
diff --git a/test/fixtures/es-module-specifiers/package-type-module/c.cjs b/test/fixtures/es-module-specifiers/package-type-module/c.cjs
new file mode 100644
index 0000000000..2d5312952f
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/c.cjs
@@ -0,0 +1,5 @@
+module.exports = {
+  one: 1,
+  two: 2,
+  three: 3
+};
diff --git a/test/fixtures/es-module-specifiers/package-type-module/index.js b/test/fixtures/es-module-specifiers/package-type-module/index.js
new file mode 100644
index 0000000000..a8baacb7c9
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/index.js
@@ -0,0 +1,21 @@
+// ESM with only default
+import a from './a.js';
+// ESM with named export
+import {b} from './b.mjs';
+// import 'c.cjs';
+import cjs from './c.cjs';
+// import across boundaries
+import jsAsCjs from '../package-type-commonjs/a.js'
+
+// named export from core
+import {strictEqual, deepStrictEqual} from 'assert';
+
+strictEqual(a, jsAsCjs);
+strictEqual(b, 'b');
+deepStrictEqual(cjs, {
+  one: 1,
+  two: 2,
+  three: 3
+});
+
+export default 'module';
diff --git a/test/fixtures/es-module-specifiers/package-type-module/package.json b/test/fixtures/es-module-specifiers/package-type-module/package.json
new file mode 100644
index 0000000000..3dbc1ca591
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package-type-module/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/test/fixtures/es-module-specifiers/package.json b/test/fixtures/es-module-specifiers/package.json
new file mode 100644
index 0000000000..9e26dfeeb6
--- /dev/null
+++ b/test/fixtures/es-module-specifiers/package.json
@@ -0,0 +1 @@
+{}
\ No newline at end of file
diff --git a/test/fixtures/es-modules/cjs-file.cjs b/test/fixtures/es-modules/cjs-file.cjs
new file mode 100644
index 0000000000..3d0637686e
--- /dev/null
+++ b/test/fixtures/es-modules/cjs-file.cjs
@@ -0,0 +1 @@
+console.log('.cjs file');
diff --git a/test/fixtures/es-modules/json-cache/another.cjs b/test/fixtures/es-modules/json-cache/another.cjs
new file mode 100644
index 0000000000..8c8e9f1c0f
--- /dev/null
+++ b/test/fixtures/es-modules/json-cache/another.cjs
@@ -0,0 +1,7 @@
+const test = require('./test.json');
+
+module.exports = {
+  ...test
+};
+
+test.one = 'it comes';
diff --git a/test/fixtures/es-modules/json-cache/mod.cjs b/test/fixtures/es-modules/json-cache/mod.cjs
new file mode 100644
index 0000000000..047cfb24a4
--- /dev/null
+++ b/test/fixtures/es-modules/json-cache/mod.cjs
@@ -0,0 +1,7 @@
+const test = require('./test.json');
+
+module.exports = {
+  ...test
+};
+
+test.one = 'zalgo';
diff --git a/test/fixtures/es-modules/json-cache/test.json b/test/fixtures/es-modules/json-cache/test.json
new file mode 100644
index 0000000000..120cbb2840
--- /dev/null
+++ b/test/fixtures/es-modules/json-cache/test.json
@@ -0,0 +1,5 @@
+{
+  "one": 1,
+  "two": 2,
+  "three": 3
+}
diff --git a/test/fixtures/es-modules/json.json b/test/fixtures/es-modules/json.json
deleted file mode 100644
index 8288d42e2b..0000000000
--- a/test/fixtures/es-modules/json.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "val": 42
-}
diff --git a/test/fixtures/es-modules/loop.mjs b/test/fixtures/es-modules/loop.mjs
index 1b5cab10ed..3d2ddd2eb7 100644
--- a/test/fixtures/es-modules/loop.mjs
+++ b/test/fixtures/es-modules/loop.mjs
@@ -1,4 +1,4 @@
-import { message } from './message';
+import { message } from './message.mjs';
 
 var t = 1;
 var k = 1;
diff --git a/test/fixtures/es-modules/mjs-file.mjs b/test/fixtures/es-modules/mjs-file.mjs
new file mode 100644
index 0000000000..489d4ab570
--- /dev/null
+++ b/test/fixtures/es-modules/mjs-file.mjs
@@ -0,0 +1 @@
+console.log('.mjs file');
diff --git a/test/fixtures/es-modules/noext-esm b/test/fixtures/es-modules/noext-esm
new file mode 100644
index 0000000000..251d6e538a
--- /dev/null
+++ b/test/fixtures/es-modules/noext-esm
@@ -0,0 +1,2 @@
+export default 'module';
+console.log('executed');
diff --git a/test/fixtures/es-modules/package-type-commonjs/index.js b/test/fixtures/es-modules/package-type-commonjs/index.js
new file mode 100644
index 0000000000..009431d851
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-commonjs/index.js
@@ -0,0 +1,3 @@
+const identifier = 'package-type-commonjs';
+console.log(identifier);
+module.exports = identifier;
diff --git a/test/fixtures/es-modules/package-type-commonjs/package.json b/test/fixtures/es-modules/package-type-commonjs/package.json
new file mode 100644
index 0000000000..4aaa4a2388
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-commonjs/package.json
@@ -0,0 +1,4 @@
+{
+  "type": "commonjs",
+  "main": "index.js"
+}
diff --git a/test/fixtures/es-modules/package-type-module/index.js b/test/fixtures/es-modules/package-type-module/index.js
new file mode 100644
index 0000000000..12aba970ef
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-module/index.js
@@ -0,0 +1,3 @@
+const identifier = 'package-type-module';
+console.log(identifier);
+export default identifier;
diff --git a/test/fixtures/es-modules/package-type-module/package.json b/test/fixtures/es-modules/package-type-module/package.json
new file mode 100644
index 0000000000..07aec65d5a
--- /dev/null
+++ b/test/fixtures/es-modules/package-type-module/package.json
@@ -0,0 +1,4 @@
+{
+  "type": "module",
+  "main": "index.js"
+}
diff --git a/test/fixtures/es-modules/package-without-type/index.js b/test/fixtures/es-modules/package-without-type/index.js
new file mode 100644
index 0000000000..a547216cb0
--- /dev/null
+++ b/test/fixtures/es-modules/package-without-type/index.js
@@ -0,0 +1,3 @@
+const identifier = 'package-without-type';
+console.log(identifier);
+module.exports = identifier;
diff --git a/test/fixtures/es-modules/package-without-type/package.json b/test/fixtures/es-modules/package-without-type/package.json
new file mode 100644
index 0000000000..14ab704d8f
--- /dev/null
+++ b/test/fixtures/es-modules/package-without-type/package.json
@@ -0,0 +1,3 @@
+{
+  "main": "index.js"
+}
diff --git a/test/fixtures/es-modules/pjson-main/main.js b/test/fixtures/es-modules/pjson-main/main.js
deleted file mode 100644
index dfdd47b877..0000000000
--- a/test/fixtures/es-modules/pjson-main/main.js
+++ /dev/null
@@ -1 +0,0 @@
-module.exports = 'main';
diff --git a/test/fixtures/es-modules/pjson-main/main.mjs b/test/fixtures/es-modules/pjson-main/main.mjs
new file mode 100644
index 0000000000..9eb0aade18
--- /dev/null
+++ b/test/fixtures/es-modules/pjson-main/main.mjs
@@ -0,0 +1 @@
+export const main = 'main'
diff --git a/test/fixtures/es-modules/pjson-main/package.json b/test/fixtures/es-modules/pjson-main/package.json
index c13b8cf6ac..ea9b784692 100644
--- a/test/fixtures/es-modules/pjson-main/package.json
+++ b/test/fixtures/es-modules/pjson-main/package.json
@@ -1,3 +1,3 @@
 {
-  "main": "main.js"
+  "main": "main.mjs"
 }
diff --git a/test/fixtures/es-modules/test-esm-double-encoding-native%20.js b/test/fixtures/es-modules/test-esm-double-encoding-native%20.mjs
index ea1caa81be..a3bfe972e5 100644
--- a/test/fixtures/es-modules/test-esm-double-encoding-native%20.js
+++ b/test/fixtures/es-modules/test-esm-double-encoding-native%20.mjs
@@ -3,4 +3,4 @@
 // Trivial test to assert we can load files with `%` in their pathname.
 // Imported by `test-esm-double-encoding.mjs`.
 
-module.exports = 42;
+export default 42;
diff --git a/test/fixtures/experimental.json b/test/fixtures/experimental.json
new file mode 100644
index 0000000000..12611d2385
--- /dev/null
+++ b/test/fixtures/experimental.json
@@ -0,0 +1,3 @@
+{
+  "ofLife": 42
+}
diff --git a/test/fixtures/syntax/bad_syntax.mjs b/test/fixtures/syntax/bad_syntax.mjs
new file mode 100644
index 0000000000..c2cd118b23
--- /dev/null
+++ b/test/fixtures/syntax/bad_syntax.mjs
@@ -0,0 +1 @@
+var foo bar;
diff --git a/test/message/esm_display_syntax_error.out b/test/message/esm_display_syntax_error.out
index 1c68ecb952..5e82a1e1ee 100644
--- a/test/message/esm_display_syntax_error.out
+++ b/test/message/esm_display_syntax_error.out
@@ -2,6 +2,7 @@
 file:///*/test/message/esm_display_syntax_error.mjs:3
 await async () => 0;
 ^^^^^
+
 SyntaxError: Unexpected reserved word
-    at internal/modules/esm/translators.js:*:*
+    at Loader.moduleStrategy (internal/modules/esm/translators.js:*:*)
     at async link (internal/modules/esm/module_job.js:*:*)
diff --git a/test/message/esm_display_syntax_error_import.mjs b/test/message/esm_display_syntax_error_import.mjs
index 87cedf1d4e..12d10270e9 100644
--- a/test/message/esm_display_syntax_error_import.mjs
+++ b/test/message/esm_display_syntax_error_import.mjs
@@ -1,7 +1,7 @@
 // Flags:  --experimental-modules
-/* eslint-disable no-unused-vars */
-import '../common';
+/* eslint-disable no-unused-vars, node-core/required-modules */
+import '../common/index.mjs';
 import {
   foo,
   notfound
-} from '../fixtures/es-module-loaders/module-named-exports';
+} from '../fixtures/es-module-loaders/module-named-exports.mjs';
diff --git a/test/message/esm_display_syntax_error_import.out b/test/message/esm_display_syntax_error_import.out
index edbbde9f2d..a3601d6cb4 100644
--- a/test/message/esm_display_syntax_error_import.out
+++ b/test/message/esm_display_syntax_error_import.out
@@ -2,7 +2,7 @@
 file:///*/test/message/esm_display_syntax_error_import.mjs:6
   notfound
   ^^^^^^^^
-SyntaxError: The requested module '../fixtures/es-module-loaders/module-named-exports' does not provide an export named 'notfound'
+SyntaxError: The requested module '../fixtures/es-module-loaders/module-named-exports.mjs' does not provide an export named 'notfound'
     at ModuleJob._instantiate (internal/modules/esm/module_job.js:*:*)
     at async ModuleJob.run (internal/modules/esm/module_job.js:*:*)
     at async Loader.import (internal/modules/esm/loader.js:*:*)
diff --git a/test/message/esm_display_syntax_error_import_module.mjs b/test/message/esm_display_syntax_error_import_module.mjs
index 32c0edb350..a53bbbcd19 100644
--- a/test/message/esm_display_syntax_error_import_module.mjs
+++ b/test/message/esm_display_syntax_error_import_module.mjs
@@ -1,3 +1,4 @@
 // Flags:  --experimental-modules
-import '../common';
-import '../fixtures/es-module-loaders/syntax-error-import';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import '../fixtures/es-module-loaders/syntax-error-import.mjs';
diff --git a/test/message/esm_display_syntax_error_import_module.out b/test/message/esm_display_syntax_error_import_module.out
index 0512a9ac77..0daaeff5b9 100644
--- a/test/message/esm_display_syntax_error_import_module.out
+++ b/test/message/esm_display_syntax_error_import_module.out
@@ -1,8 +1,8 @@
 (node:*) ExperimentalWarning: The ESM module loader is experimental.
 file:///*/test/fixtures/es-module-loaders/syntax-error-import.mjs:1
-import { foo, notfound } from './module-named-exports';
+import { foo, notfound } from './module-named-exports.mjs';
               ^^^^^^^^
-SyntaxError: The requested module './module-named-exports' does not provide an export named 'notfound'
+SyntaxError: The requested module './module-named-exports.mjs' does not provide an export named 'notfound'
     at ModuleJob._instantiate (internal/modules/esm/module_job.js:*:*)
     at async ModuleJob.run (internal/modules/esm/module_job.js:*:*)
     at async Loader.import (internal/modules/esm/loader.js:*:*)
diff --git a/test/message/esm_display_syntax_error_module.mjs b/test/message/esm_display_syntax_error_module.mjs
index e74b70bec8..5905d2a954 100644
--- a/test/message/esm_display_syntax_error_module.mjs
+++ b/test/message/esm_display_syntax_error_module.mjs
@@ -1,3 +1,4 @@
 // Flags:  --experimental-modules
-import '../common';
-import '../fixtures/es-module-loaders/syntax-error';
+/* eslint-disable node-core/required-modules */
+import '../common/index.mjs';
+import '../fixtures/es-module-loaders/syntax-error.mjs';
diff --git a/test/message/esm_display_syntax_error_module.out b/test/message/esm_display_syntax_error_module.out
index 4e4cbf2ea3..a1498f72c9 100644
--- a/test/message/esm_display_syntax_error_module.out
+++ b/test/message/esm_display_syntax_error_module.out
@@ -2,5 +2,6 @@
 file:///*/test/fixtures/es-module-loaders/syntax-error.mjs:2
 await async () => 0;
 ^^^^^
+
 SyntaxError: Unexpected reserved word
-    at internal/modules/esm/translators.js:*:*
+    at Loader.moduleStrategy (internal/modules/esm/translators.js:*:*)
\ No newline at end of file
diff --git a/test/parallel/test-cli-syntax-piped-bad.js b/test/parallel/test-cli-syntax-piped-bad.js
index 4fb24b24f3..6d6f800a40 100644
--- a/test/parallel/test-cli-syntax-piped-bad.js
+++ b/test/parallel/test-cli-syntax-piped-bad.js
@@ -8,24 +8,45 @@ const node = process.execPath;
 
 // Test both sets of arguments that check syntax
 const syntaxArgs = [
-  ['-c'],
-  ['--check']
+  '-c',
+  '--check'
 ];
 
 // Match on the name of the `Error` but not the message as it is different
 // depending on the JavaScript engine.
-const syntaxErrorRE = /^SyntaxError: \b/m;
+const syntaxErrorRE = /^SyntaxError: Unexpected identifier\b/m;
 
 // Should throw if code piped from stdin with --check has bad syntax
 // loop each possible option, `-c` or `--check`
-syntaxArgs.forEach(function(args) {
+syntaxArgs.forEach(function(arg) {
   const stdin = 'var foo bar;';
-  const c = spawnSync(node, args, { encoding: 'utf8', input: stdin });
+  const c = spawnSync(node, [arg], { encoding: 'utf8', input: stdin });
 
   // stderr should include '[stdin]' as the filename
   assert(c.stderr.startsWith('[stdin]'), `${c.stderr} starts with ${stdin}`);
 
-  // No stdout or stderr should be produced
+  // No stdout should be produced
+  assert.strictEqual(c.stdout, '');
+
+  // stderr should have a syntax error message
+  assert(syntaxErrorRE.test(c.stderr), `${syntaxErrorRE} === ${c.stderr}`);
+
+  assert.strictEqual(c.status, 1);
+});
+
+// Check --entry-type=module
+syntaxArgs.forEach(function(arg) {
+  const stdin = 'export var p = 5; var foo bar;';
+  const c = spawnSync(
+    node,
+    ['--experimental-modules', '--entry-type=module', '--no-warnings', arg],
+    { encoding: 'utf8', input: stdin }
+  );
+
+  // stderr should include '[stdin]' as the filename
+  assert(c.stderr.startsWith('[stdin]'), `${c.stderr} starts with ${stdin}`);
+
+  // No stdout should be produced
   assert.strictEqual(c.stdout, '');
 
   // stderr should have a syntax error message
diff --git a/test/parallel/test-cli-syntax-piped-good.js b/test/parallel/test-cli-syntax-piped-good.js
index cdadf449d8..b2b02172cb 100644
--- a/test/parallel/test-cli-syntax-piped-good.js
+++ b/test/parallel/test-cli-syntax-piped-good.js
@@ -8,15 +8,31 @@ const node = process.execPath;
 
 // Test both sets of arguments that check syntax
 const syntaxArgs = [
-  ['-c'],
-  ['--check']
+  '-c',
+  '--check'
 ];
 
 // Should not execute code piped from stdin with --check.
 // Loop each possible option, `-c` or `--check`.
-syntaxArgs.forEach(function(args) {
+syntaxArgs.forEach(function(arg) {
   const stdin = 'throw new Error("should not get run");';
-  const c = spawnSync(node, args, { encoding: 'utf8', input: stdin });
+  const c = spawnSync(node, [arg], { encoding: 'utf8', input: stdin });
+
+  // No stdout or stderr should be produced
+  assert.strictEqual(c.stdout, '');
+  assert.strictEqual(c.stderr, '');
+
+  assert.strictEqual(c.status, 0);
+});
+
+// Check --entry-type=module
+syntaxArgs.forEach(function(arg) {
+  const stdin = 'export var p = 5; throw new Error("should not get run");';
+  const c = spawnSync(
+    node,
+    ['--experimental-modules', '--no-warnings', '--entry-type=module', arg],
+    { encoding: 'utf8', input: stdin }
+  );
 
   // No stdout or stderr should be produced
   assert.strictEqual(c.stdout, '');
diff --git a/test/parallel/test-loaders-unknown-builtin-module.mjs b/test/parallel/test-loaders-unknown-builtin-module.mjs
index db3cfa3582..5f47f191f5 100644
--- a/test/parallel/test-loaders-unknown-builtin-module.mjs
+++ b/test/parallel/test-loaders-unknown-builtin-module.mjs
@@ -1,5 +1,6 @@
 // Flags: --experimental-modules --loader ./test/fixtures/es-module-loaders/loader-unknown-builtin-module.mjs
-import { expectsError, mustCall } from '../common';
+/* eslint-disable node-core/required-modules */
+import { expectsError, mustCall } from '../common/index.mjs';
 import assert from 'assert';
 
 const unknownBuiltinModule = 'unknown-builtin-module';
diff --git a/test/parallel/test-module-main-extension-lookup.js b/test/parallel/test-module-main-extension-lookup.js
index 3d20316647..9e7eab295e 100644
--- a/test/parallel/test-module-main-extension-lookup.js
+++ b/test/parallel/test-module-main-extension-lookup.js
@@ -6,6 +6,6 @@ const { execFileSync } = require('child_process');
 const node = process.argv[0];
 
 execFileSync(node, ['--experimental-modules',
-                    fixtures.path('es-modules', 'test-esm-ok')]);
+                    fixtures.path('es-modules', 'test-esm-ok.mjs')]);
 execFileSync(node, ['--experimental-modules',
                     fixtures.path('es-modules', 'noext')]);