feat: ESM configuration file

lib/cli/config.js

@@ -24,6 +24,7 @@ const utils = require("../utils");
 exports.CONFIG_FILES = [
   ".mocharc.cjs",
   ".mocharc.js",
+  ".mocharc.mjs",
   ".mocharc.yaml",
   ".mocharc.yml",
   ".mocharc.jsonc",
@@ -72,6 +73,9 @@ exports.loadConfig = (filepath) => {
   try {
     if (ext === ".yml" || ext === ".yaml") {
       config = parsers.yaml(filepath);
+    } else if (ext === ".js" || ext === ".cjs" || ext === ".mjs") {
+      const parsedConfig = parsers.js(filepath);
+      config = parsedConfig.default ?? parsedConfig;
     } else if (ext === ".js" || ext === ".cjs") {
       config = parsers.js(filepath);
     } else {

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", js);
     expect(json, "to equal", yaml);
   });
 

test/integration/fixtures/config/mocharc.mjs

@@ -0,0 +1,7 @@
+// a comment
+export default {
+  require: ['foo', 'bar'],
+  bail: true,
+  reporter: 'dot',
+  slow: 60
+};

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

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