updating resolve.extensions to include webpack4 default extensions

Author: weaverryan

fixtures/js/hello_world.mjs

@@ -0,0 +1 @@
+document.getElementById('app').innerHTML = 'Hello World!';

lib/config-generator.js

@@ -92,7 +92,7 @@ class ConfigGenerator {
         config.stats = this.buildStatsConfig();
 
         config.resolve = {
-            extensions: ['.js', '.jsx', '.vue', '.ts', '.tsx'],
+            extensions: ['.wasm', '.mjs', '.js', '.json', '.jsx', '.vue', '.ts', '.tsx'],
             alias: Object.assign({}, this.webpackConfig.aliases)
         };
 

test/functional.js

@@ -1743,6 +1743,22 @@ module.exports = {
                     done();
                 });
             });
+
+            it('.mjs files are supported natively', (done) => {
+                const config = createWebpackConfig('web/build', 'dev');
+                config.addEntry('main', './js/hello_world');
+                config.setPublicPath('/build');
+
+                testSetup.runWebpack(config, (webpackAssert) => {
+                    // check that main.js has the correct contents
+                    webpackAssert.assertOutputFileContains(
+                        'main.js',
+                        'Hello World!'
+                    );
+
+                    done();
+                });
+            });
         });
     });
 });