Feature: ESM configuration file

lib/cli/config.js

@@ -24,30 +24,45 @@ const utils = require('../utils');
 exports.CONFIG_FILES = [
   '.mocharc.cjs',
   '.mocharc.js',
+  '.mocharc.mjs',
   '.mocharc.yaml',
   '.mocharc.yml',
   '.mocharc.jsonc',
   '.mocharc.json'
 ];
 
+/**
+ * Loads a CommonJS or ESM module, resolving its path if the file path is not
+ * relative
+ *
+ * @param {string} filepath - Module file path to load
+ * @returns {Object} CommonJS or ESM module
+ */
+const loadModule = filepath => {
+  let cwdFilepath;
+  try {
+    debug('parsers: load cwd-relative path: "%s"', path.resolve(filepath));
+    cwdFilepath = require.resolve(path.resolve(filepath)); // evtl. throws
+    return require(cwdFilepath);
+  } catch (err) {
+    if (cwdFilepath) throw err;
+
+    debug('parsers: retry load as module-relative path: "%s"', filepath);
+    return require(filepath);
+  }
+};
+
 /**
  * Parsers for various config filetypes. Each accepts a filepath and
  * returns an object (but could throw)
  */
 const parsers = (exports.parsers = {
   yaml: filepath => require('js-yaml').load(fs.readFileSync(filepath, 'utf8')),
-  js: filepath => {
-    let cwdFilepath;
-    try {
-      debug('parsers: load cwd-relative path: "%s"', path.resolve(filepath));
-      cwdFilepath = require.resolve(path.resolve(filepath)); // evtl. throws
-      return require(cwdFilepath);
-    } catch (err) {
-      if (cwdFilepath) throw err;
+  js: loadModule,
+  mjs: filepath => {
+    const module = loadModule(filepath);
 
-      debug('parsers: retry load as module-relative path: "%s"', filepath);
-      return require(filepath);
-    }
+    return module.default ?? module;
   },
   json: filepath =>
     JSON.parse(
@@ -73,7 +88,9 @@ exports.loadConfig = filepath => {
       config = parsers.yaml(filepath);
     } else if (ext === '.js' || ext === '.cjs') {
       config = parsers.js(filepath);
-    } else {
+    } else if (ext === '.mjs') {
+      config = parsers.mjs(filepath);
+    }else {
       config = parsers.json(filepath);
     }
   } catch (err) {

test/integration/config.spec.js

@@ -12,10 +12,12 @@ describe('config', function () {
     var configDir = path.join(__dirname, 'fixtures', 'config');
     var js = loadConfig(path.join(configDir, 'mocharc.js'));
     var cjs = loadConfig(path.join(configDir, 'mocharc.cjs'));
+    var mjs = loadConfig(path.join(configDir, 'mocharc.mjs'));
     var json = loadConfig(path.join(configDir, 'mocharc.json'));
     var yaml = loadConfig(path.join(configDir, 'mocharc.yaml'));
     expect(js, 'to equal', json);
     expect(js, 'to equal', cjs);
+    expect(mjs, 'to equal', cjs);
     expect(json, 'to equal', yaml);
   });
 

test/integration/fixtures/config/mocharc.mjs

@@ -0,0 +1,9 @@
+'use strict';
+
+// a comment
+export default {
+  require: ['foo', 'bar'],
+  bail: true,
+  reporter: 'dot',
+  slow: 60
+};

test/node-unit/cli/config.spec.js

@@ -28,6 +28,7 @@ describe('cli/config', function () {
         sinon.stub(parsers, 'yaml').returns(phonyConfigObject);
         sinon.stub(parsers, 'json').returns(phonyConfigObject);
         sinon.stub(parsers, 'js').returns(phonyConfigObject);
+        sinon.stub(parsers, 'mjs').returns(phonyConfigObject);
       });
 
       describe('when supplied a filepath with ".yaml" extension', function () {
@@ -74,6 +75,17 @@ describe('cli/config', function () {
         });
       });
 
+      describe('when supplied a filepath with ".mjs" extension', function () {
+        const filepath = 'foo.mjs';
+
+        it('should use the MJS parser', function () {
+          loadConfig(filepath);
+          expect(parsers.mjs, 'to have calls satisfying', [
+            {args: [filepath], returned: phonyConfigObject}
+          ]).and('was called once');
+        });
+      });
+
       describe('when supplied a filepath with ".jsonc" extension', function () {
         const filepath = 'foo.jsonc';