module: proxy require('esm') to import('esm')

Author: MylesBorins

lib/internal/errors.js

@@ -1396,26 +1396,6 @@ E('ERR_PACKAGE_PATH_NOT_EXPORTED', (pkgPath, subpath, base = undefined) => {
 E('ERR_PERFORMANCE_INVALID_TIMESTAMP',
   '%d is not a valid timestamp', TypeError);
 E('ERR_PERFORMANCE_MEASURE_INVALID_OPTIONS', '%s', TypeError);
-E('ERR_REQUIRE_ESM',
-  (filename, parentPath = null, packageJsonPath = null) => {
-    let msg = `Must use import to load ES Module: ${filename}`;
-    if (parentPath && packageJsonPath) {
-      const path = require('path');
-      const basename = path.basename(filename) === path.basename(parentPath) ?
-        filename : path.basename(filename);
-      msg +=
-        '\nrequire() of ES modules is not supported.\nrequire() of ' +
-        `${filename} from ${parentPath} ` +
-        'is an ES module file as it is a .js file whose nearest parent ' +
-        'package.json contains "type": "module" which defines all .js ' +
-        'files in that package scope as ES modules.\nInstead rename ' +
-        `${basename} to end in .cjs, change the requiring code to use ` +
-        'import(), or remove "type": "module" from ' +
-        `${packageJsonPath}.\n`;
-      return msg;
-    }
-    return msg;
-  }, Error);
 E('ERR_SCRIPT_EXECUTION_INTERRUPTED',
   'Script execution was interrupted by `SIGINT`', Error);
 E('ERR_SERVER_ALREADY_LISTEN',

lib/internal/modules/cjs/loader.js

@@ -111,7 +111,6 @@ let hasLoadedAnyUserCJSModule = false;
 const {
   ERR_INVALID_ARG_VALUE,
   ERR_INVALID_MODULE_SPECIFIER,
-  ERR_REQUIRE_ESM,
   ERR_UNKNOWN_BUILTIN_MODULE,
 } = require('internal/errors').codes;
 const { validateString } = require('internal/validators');
@@ -983,8 +982,17 @@ Module.prototype.load = function(filename) {
 
   const extension = findLongestRegisteredExtension(filename);
   // allow .mjs to be overridden
-  if (StringPrototypeEndsWith(filename, '.mjs') && !Module._extensions['.mjs'])
-    throw new ERR_REQUIRE_ESM(filename);
+  if (StringPrototypeEndsWith(filename, '.mjs') &&
+    !Module._extensions['.mjs']) {
+    process.emitWarning('Attempting to require and ESModule.' +
+                        'Replace `require` with `import`',
+                        'Warning', 'WARN_REQUIRE_ESM');
+    const ESMLoader = asyncESM.ESMLoader;
+    const exports = ESMLoader.import(filename);
+    this.exports = exports;
+    this.loaded = true;
+    return;
+  }
 
   Module._extensions[extension](this, filename);
   this.loaded = true;
@@ -1120,10 +1128,14 @@ Module._extensions['.js'] = function(module, filename) {
     const pkg = readPackageScope(filename);
     // Function require shouldn't be used in ES modules.
     if (pkg?.data?.type === 'module') {
-      const parent = moduleParentCache.get(module);
-      const parentPath = parent?.filename;
-      const packageJsonPath = path.resolve(pkg.path, 'package.json');
-      throw new ERR_REQUIRE_ESM(filename, parentPath, packageJsonPath);
+      process.emitWarning('Attempting to require and ESModule.' +
+                          'Replace `require` with `import`',
+                          'Warning', 'WARN_REQUIRE_ESM');
+      const ESMLoader = asyncESM.ESMLoader;
+      const exports = ESMLoader.import(filename);
+      module.exports = exports;
+      module.loaded = true;
+      return;
     }
   }
   // If already analyzed the source, then it will be cached.

test/es-module/test-cjs-esm-warn.js

@@ -23,16 +23,6 @@ expect('', packageWithoutTypeMain, 'package-without-type');
 expect('--input-type=module', packageTypeModuleMain,
        'ERR_INPUT_TYPE_NOT_ALLOWED', true);
 
-try {
-  require('../fixtures/es-modules/package-type-module/index.js');
-  assert.fail('Expected CJS to fail loading from type: module package.');
-} catch (e) {
-  assert.strictEqual(e.name, 'Error');
-  assert.strictEqual(e.code, 'ERR_REQUIRE_ESM');
-  assert(e.toString().match(/Must use import to load ES Module/g));
-  assert(e.message.match(/Must use import to load ES Module/g));
-}
-
 function expect(opt = '', inputFile, want, wantsError = false) {
   const argv = [inputFile];
   const opts = {

test/es-module/test-esm-type-flag-errors.js

@@ -1,11 +1,22 @@
 'use strict';
-require('../common');
+const { expectWarning } = require('../common');
 const assert = require('assert');
 
-assert.throws(
-  () => require('../fixtures/es-modules/test-esm-ok.mjs'),
-  {
-    message: /Must use import to load ES Module/,
-    code: 'ERR_REQUIRE_ESM'
-  }
-);
+expectWarning('Warning', [
+  [
+    'Attempting to require and ESModule. Replace `require` with `import`',
+    'WARN_REQUIRE_ESM',
+  ],
+  [
+    'Attempting to require and ESModule. Replace `require` with `import`',
+    'WARN_REQUIRE_ESM',
+  ],
+]);
+
+require('../fixtures/es-modules/test-esm-ok.mjs').then((module) => {
+  assert.ok(module.default);
+});
+
+require('../fixtures/es-modules/package-type-module').then((module) => {
+  assert.strictEqual(module.default, 'package-type-module');
+});