1 files changed, 61 insertions, 0 deletions
diff --git a/lib/internal/modules/esm/CreateDynamicModule.js b/lib/internal/modules/esm/CreateDynamicModule.js
new file mode 100644
index 0000000000..7e9777af51
--- /dev/null
+++ b/lib/internal/modules/esm/CreateDynamicModule.js
@@ -0,0 +1,61 @@
+'use strict';
+
+const { internalBinding } = require('internal/bootstrap/loaders');
+const { ModuleWrap } = internalBinding('module_wrap');
+const debug = require('util').debuglog('esm');
+const ArrayJoin = Function.call.bind(Array.prototype.join);
+const ArrayMap = Function.call.bind(Array.prototype.map);
+
+const createDynamicModule = (exports, url = '', evaluate) => {
+  debug(
+    `creating ESM facade for ${url} with exports: ${ArrayJoin(exports, ', ')}`
+  );
+  const names = ArrayMap(exports, (name) => `${name}`);
+  // Create two modules: One whose exports are get- and set-able ('reflective'),
+  // and one which re-exports all of these but additionally may
+  // run an executor function once everything is set up.
+  const src = `
+  export let executor;
+  ${ArrayJoin(ArrayMap(names, (name) => `export let $${name};`), '\n')}
+  /* This function is implicitly returned as the module's completion value */
+  (() => ({
+    setExecutor: fn => executor = fn,
+    reflect: {
+      exports: { ${
+  ArrayJoin(ArrayMap(names, (name) => `
+        ${name}: {
+          get: () => $${name},
+          set: v => $${name} = v
+        }`), ', \n')}
+      }
+    }
+  }));`;
+  const reflectiveModule = new ModuleWrap(src, `cjs-facade:${url}`);
+  reflectiveModule.instantiate();
+  const { setExecutor, reflect } = reflectiveModule.evaluate()();
+  // public exposed ESM
+  const reexports = `
+  import {
+    executor,
+    ${ArrayMap(names, (name) => `$${name}`)}
+  } from "";
+  export {
+    ${ArrayJoin(ArrayMap(names, (name) => `$${name} as ${name}`), ', ')}
+  }
+  if (typeof executor === "function") {
+    // add await to this later if top level await comes along
+    executor()
+  }`;
+  if (typeof evaluate === 'function') {
+    setExecutor(() => evaluate(reflect));
+  }
+  const module = new ModuleWrap(reexports, `${url}`);
+  module.link(async () => reflectiveModule);
+  module.instantiate();
+  return {
+    module,
+    reflect
+  };
+};
+
+module.exports = createDynamicModule;