fix: load mjs files correctly (#5429)

Author: mark-wiemer

eslint.config.js

@@ -71,7 +71,7 @@ module.exports = [
   },
   {
     files: [
-      'test/compiler-esm/*.js'
+      'test/compiler-esm/*.{js,mjs}'
     ],
     languageOptions: {
       sourceType: 'module',

lib/nodejs/esm-utils.js

@@ -90,14 +90,19 @@ const tryImportAndRequire = async (file, esmDecorator) => {
 // and `require.cache` effective, while allowing us to load ESM modules
 // and CJS modules in the same way.
 const requireModule = async (file, esmDecorator) => {
+  if (path.extname(file) === '.mjs') {
+    return formattedImport(file, esmDecorator);
+  }
   try {
     return require(file);
   } catch (err) {
     // Import if require fails.
     return dealWithExports(await formattedImport(file, esmDecorator));
   }
-}
+};
 
+// We only assign this `requireOrImport` function once based on Node version
+// We check for file extensions in `requireModule` and `tryImportAndRequire`
 if (process.features.require_module) {
   exports.requireOrImport = requireModule;
 } else {

test/compiler-esm/test-tla.mjs

@@ -0,0 +1,11 @@
+const obj = { foo: 'bar' };
+
+describe('esm written in esm with top-level-await', () => {
+  it('should work', () => {
+    expect(obj, 'to equal', { foo: 'bar' });
+  });
+});
+
+await undefined;
+
+export const foo = 'bar';

test/compiler-esm/test-tla.mjs.compiled

@@ -0,0 +1,11 @@
+const obj = { foo: 'bar' };
+
+describe('esm written in esm with top-level-await', () => {
+  it('should work', () => {
+    expect(obj, 'to equal', { foo: 'bar' });
+  });
+});
+
+await undefined;
+
+export const foo = 'bar';

test/compiler-esm/test.mjs

@@ -0,0 +1,9 @@
+const obj = {foo: 'bar'};
+
+describe('esm written in esm', () => {
+  it('should work', () => {
+    expect(obj, 'to equal', {foo: 'bar'});
+  });
+});
+
+export const foo = 'bar';

test/compiler-esm/test.mjs.compiled

@@ -0,0 +1,9 @@
+const obj = {foo: 'bar'};
+
+describe('esm written in esm', () => {
+  it('should work', () => {
+    expect(obj, 'to equal', {foo: 'bar'});
+  });
+});
+
+export const foo = 'bar';

test/integration/compiler-esm-only-loader.spec.js

@@ -5,13 +5,18 @@ var path = require('node:path');
 
 // Regression test for https://github.com/mochajs/mocha/issues/5380
 describe('support ESM only module loader packages', function () {
-  it('should support ESM .js extension', function (done) {
+  /**
+   * Load the filename using an ESM-only loader and expect things to work
+   * @param {string} filename Name of the file to load
+   * @param {Function} done A Mocha done callback for when the test ends
+   */
+  function loadAndExpect(filename, done) {
     exec(
       '"' +
         process.execPath +
         '" "' +
         path.join('bin', 'mocha') +
-        '" -R json --require "@test/esm-only-loader" "test/compiler-esm/*.js"',
+        `" -R json --require "@test/esm-only-loader" "${filename}"`,
       {cwd: path.join(__dirname, '..', '..')},
       function (error, stdout) {
         if (error && !stdout) {
@@ -24,48 +29,26 @@ describe('support ESM only module loader packages', function () {
           expect(results.tests[index], 'to have property', 'fullTitle');
           titles.push(results.tests[index].fullTitle);
         }
-        expect(
-          titles,
-          'to contain',
-          'esm written in esm should work',
-        ).and(
-          'to contain',
-          'esm written in esm with top-level-await should work',
-        ).and('to have length', 2);
+        expect(titles, 'to contain', 'esm written in esm should work')
+          .and(
+            'to contain',
+            'esm written in esm with top-level-await should work'
+          )
+          .and('to have length', 2);
         done();
       }
     );
+  }
+
+  it('should support ESM .js extension', function (done) {
+    loadAndExpect('test/compiler-esm/*.js', done);
   });
 
   it('should support ESM .ts extension', function (done) {
-    exec(
-      '"' +
-        process.execPath +
-        '" "' +
-        path.join('bin', 'mocha') +
-        '" -R json --require "@test/esm-only-loader" "test/compiler-esm/*.ts"',
-      {cwd: path.join(__dirname, '..', '..')},
-      function (error, stdout) {
-        if (error && !stdout) {
-          return done(error);
-        }
-        var results = JSON.parse(stdout);
-        expect(results, 'to have property', 'tests');
-        var titles = [];
-        for (var index = 0; index < results.tests.length; index += 1) {
-          expect(results.tests[index], 'to have property', 'fullTitle');
-          titles.push(results.tests[index].fullTitle);
-        }
-        expect(
-          titles,
-          'to contain',
-          'esm written in esm should work',
-        ).and(
-          'to contain',
-          'esm written in esm with top-level-await should work',
-        ).and('to have length', 2);
-        done();
-      }
-    );
+    loadAndExpect('test/compiler-esm/*.ts', done);
+  });
+
+  it('should support ESM .mjs extension', function (done) {
+    loadAndExpect('test/compiler-esm/*.mjs', done);
   });
 });

test/integration/compiler-esm.spec.js

@@ -4,13 +4,18 @@ var exec = require('node:child_process').exec;
 var path = require('node:path');
 
 describe('support ESM module loader compilers', function () {
-  it('should support ESM .js extension', function (done) {
+  /**
+   * Runs `exec` on an ESM setup for the given file
+   * @param {string} filename Path to the file to load
+   * @param {Function} done A Mocha done callback for when the test ends
+   */
+  function loadAndExpect(filename, done) {
     exec(
       '"' +
         process.execPath +
         '" "' +
         path.join('bin', 'mocha') +
-        '" -R json --require test/compiler-fixtures/esm.fixture "test/compiler-esm/*.js"',
+        `" -R json --require test/compiler-fixtures/esm.fixture "${filename}"`,
       {cwd: path.join(__dirname, '..', '..')},
       function (error, stdout) {
         if (error && !stdout) {
@@ -23,48 +28,26 @@ describe('support ESM module loader compilers', function () {
           expect(results.tests[index], 'to have property', 'fullTitle');
           titles.push(results.tests[index].fullTitle);
         }
-        expect(
-          titles,
-          'to contain',
-          'esm written in esm should work',
-        ).and(
-          'to contain',
-          'esm written in esm with top-level-await should work',
-        ).and('to have length', 2);
+        expect(titles, 'to contain', 'esm written in esm should work')
+          .and(
+            'to contain',
+            'esm written in esm with top-level-await should work'
+          )
+          .and('to have length', 2);
         done();
       }
     );
+  }
+
+  it('should support ESM .js extension', function (done) {
+    loadAndExpect('test/compiler-esm/*.js', done);
   });
 
   it('should support ESM .ts extension', function (done) {
-    exec(
-      '"' +
-        process.execPath +
-        '" "' +
-        path.join('bin', 'mocha') +
-        '" -R json --require test/compiler-fixtures/esm.fixture "test/compiler-esm/*.ts"',
-      {cwd: path.join(__dirname, '..', '..')},
-      function (error, stdout) {
-        if (error && !stdout) {
-          return done(error);
-        }
-        var results = JSON.parse(stdout);
-        expect(results, 'to have property', 'tests');
-        var titles = [];
-        for (var index = 0; index < results.tests.length; index += 1) {
-          expect(results.tests[index], 'to have property', 'fullTitle');
-          titles.push(results.tests[index].fullTitle);
-        }
-        expect(
-          titles,
-          'to contain',
-          'esm written in esm should work',
-        ).and(
-          'to contain',
-          'esm written in esm with top-level-await should work',
-        ).and('to have length', 2);
-        done();
-      }
-    );
+    loadAndExpect('test/compiler-esm/*.ts', done);
+  });
+
+  it('should support ESM .mjs extension', function (done) {
+    loadAndExpect('test/compiler-esm/*.mjs', done);
   });
 });