change up symbol usage, use for(;;), add tests

doc/api/esm.md

@@ -86,13 +86,12 @@ or fragment string differs between `import` statements.
 CommonJS modules, when imported, will be handled in one of two ways. By default
 they will provide a single `default` export representing the value of
 `module.exports` at the time they finish evaluating. However, they may also
-provide `@@esModule` or `__esModule` to use named exports, representing each
-enumerable key of `module.exports` at the time they finish evaluating.
-`@@esModule` is available as `require('module').esModule` and prefered over
-`__esModule` In both cases, this should be thought of  like a "snapshot" of
-the exports at the time of importing; asynchronously modifying `module.exports`
-will not affect the values of the exports. Builtin libraries are provided with
-named exports as if they were using `@@esModule`.
+provide `@@esModuleInterop` or `__esModule` to use named exports, representing
+each enumerable key of `module.exports` at the time they finish evaluating.
+In both cases, this should be thought of  like a "snapshot" of the exports at
+the time of importing; asynchronously modifying `module.exports` will not
+affect the values of the exports. Builtin libraries are provided with named
+exports as if they were using `@@esModuleInterop`.
 
 ```js
 import { readFile } from 'fs';
@@ -110,9 +109,8 @@ readFile('./foo.txt', (err, body) => {
 import { part } from './other.js';
 
 // other.js
-import { esModule } from 'module';
 exports.part = () => {};
-exports[esModule] = true;
+exports[Symbol.for('esModuleInterop')] = true;
 ```
 
 ## Loader hooks

lib/internal/loader/ModuleRequest.js

@@ -19,7 +19,7 @@ const search = require('internal/loader/search');
 const asyncReadFile = require('util').promisify(require('fs').readFile);
 const debug = require('util').debuglog('esm');
 
-const esModuleSymbol = exports.esModuleSymbol = Symbol('esModule');
+const esModuleInterop = Symbol.for('esModuleInterop');
 
 const realpathCache = new Map();
 
@@ -42,12 +42,12 @@ loaders.set('cjs', async (url) => {
   const CJSModule = require('module');
   const pathname = internalURLModule.getPathFromURL(new URL(url));
   const exports = CJSModule._load(pathname);
-  const es = Boolean(exports[esModuleSymbol] || exports.__esModule);
+  const es = Boolean(exports[esModuleInterop] || exports.__esModule);
   const keys = es ? Object.keys(exports) : ['default'];
   return createDynamicModule(keys, url, (reflect) => {
     if (es) {
-      for (const key of keys)
-        reflect.exports[key].set(exports[key]);
+      for (let i = 0; i < keys.length; i++)
+        reflect.exports[keys[i]].set(exports[keys[i]]);
     } else {
       reflect.exports.default.set(exports);
     }
@@ -62,7 +62,8 @@ loaders.set('builtin', async (url) => {
   const keys = Object.keys(exports);
   return createDynamicModule(['default', ...keys], url, (reflect) => {
     reflect.exports.default.set(exports);
-    for (const key of keys) reflect.exports[key].set(exports[key]);
+    for (let i = 0; i < keys.length; i++)
+      reflect.exports[keys[i]].set(exports[keys[i]]);
   });
 });
 

lib/module.js

@@ -42,7 +42,6 @@ const errors = require('internal/errors');
 const Loader = require('internal/loader/Loader');
 const ModuleJob = require('internal/loader/ModuleJob');
 const { createDynamicModule } = require('internal/loader/ModuleWrap');
-const { esModuleSymbol } = require('internal/loader/ModuleRequest');
 let ESMLoader;
 
 function stat(filename) {
@@ -80,7 +79,6 @@ Module._pathCache = Object.create(null);
 Module._extensions = Object.create(null);
 var modulePaths = [];
 Module.globalPaths = [];
-Module.esModule = esModuleSymbol;
 
 Module.wrap = function(script) {
   return Module.wrapper[0] + script + Module.wrapper[1];

test/es-module/test-esm-cjs-esmodule.mjs

@@ -0,0 +1,9 @@
+// Flags: --experimental-modules
+/* eslint-disable required-modules */
+
+import assert from 'assert';
+import eightyfour, { named as fourtytwo } from
+  '../fixtures/es-module-loaders/babel-to-esm.js';
+
+assert.strictEqual(eightyfour, 84);
+assert.strictEqual(fourtytwo, 42);

test/fixtures/es-module-loaders/babel-to-esm.js

@@ -0,0 +1,15 @@
+"use strict";
+
+/*
+created by babel with es2015 preset
+```
+export const named = 42;
+export default 84;
+```
+*/
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+var named = exports.named = 42;
+exports.default = 84;

test/fixtures/es-module-loaders/cjs-to-es-namespace.js

@@ -1,6 +1,4 @@
-const { esModule } = require('module');
-
 exports.named = true;
 exports.default = 1;
 
-exports[esModule] = true;
+exports[Symbol.for('esModuleInterop')] = true;

test/fixtures/es-module-loaders/reserved-keywords.js

@@ -1,8 +1,6 @@
-const { esModule } = require('module');
-
 module.exports = {
   enum: 'enum',
   class: 'class',
   delete: 'delete',
-  [esModule]: true,
+  [Symbol.for('esModuleInterop')]: true,
 };