1 files changed, 30 insertions, 20 deletions

diff --git a/lib/internal/process/esm_loader.js b/lib/internal/process/esm_loader.js
index 69e1fd0016..49463e284c 100644
--- a/lib/internal/process/esm_loader.js
+++ b/lib/internal/process/esm_loader.js
@@ -3,12 +3,14 @@
 const {
   ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING,
 } = require('internal/errors').codes;
-
+const assert = require('internal/assert');
 const { Loader } = require('internal/modules/esm/loader');
 const { pathToFileURL } = require('internal/url');
 const {
   getModuleFromWrap,
 } = require('internal/vm/module');
+const { getOptionValue } = require('internal/options');
+const userLoader = getOptionValue('--experimental-loader');
 
 exports.initializeImportMetaObject = function(wrap, meta) {
   const { callbackMap } = internalBinding('module_wrap');
@@ -21,6 +23,7 @@ exports.initializeImportMetaObject = function(wrap, meta) {
 };
 
 exports.importModuleDynamicallyCallback = async function(wrap, specifier) {
+  assert(calledInitialize === true || !userLoader);
   const { callbackMap } = internalBinding('module_wrap');
   if (callbackMap.has(wrap)) {
     const { importModuleDynamically } = callbackMap.get(wrap);
@@ -32,24 +35,31 @@ exports.importModuleDynamicallyCallback = async function(wrap, specifier) {
   throw new ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING();
 };
 
-let loaderResolve;
-exports.loaderPromise = new Promise((resolve) => loaderResolve = resolve);
-
-exports.ESMLoader = undefined;
+let ESMLoader = new Loader();
+exports.ESMLoader = ESMLoader;
 
-exports.initializeLoader = function(cwd, userLoader) {
-  let ESMLoader = new Loader();
-  const loaderPromise = (async () => {
-    if (userLoader) {
-      const hooks = await ESMLoader.import(
-        userLoader, pathToFileURL(`${cwd}/`).href);
-      ESMLoader = new Loader();
-      ESMLoader.hook(hooks);
-      exports.ESMLoader = ESMLoader;
-    }
-    return ESMLoader;
+let calledInitialize = false;
+exports.initializeLoader = initializeLoader;
+async function initializeLoader() {
+  assert(calledInitialize === false);
+  calledInitialize = true;
+  if (!userLoader)
+    return;
+  let cwd;
+  try {
+    cwd = process.cwd() + '/';
+  } catch {
+    cwd = 'file:///';
+  }
+  // If --experimental-loader is specified, create a loader with user hooks.
+  // Otherwise create the default loader.
+  const { emitExperimentalWarning } = require('internal/util');
+  emitExperimentalWarning('--experimental-loader');
+  return (async () => {
+    const hooks =
+        await ESMLoader.import(userLoader, pathToFileURL(cwd).href);
+    ESMLoader = new Loader();
+    ESMLoader.hook(hooks);
+    return exports.ESMLoader = ESMLoader;
   })();
-  loaderResolve(loaderPromise);
-
-  exports.ESMLoader = ESMLoader;
-};
+}