also compile mjs files

Author: wardpeet

packages/gatsby/src/utils/webpack-utils.js

@@ -295,34 +295,16 @@ module.exports = async ({
   {
     let js = (options = {}) => {
       return {
-        test: /\.jsx?$/,
+        test: /\.(js|mjs|jsx)$/,
         exclude: /core-js|event-source-polyfill|webpack-hot-middleware\/client/,
+        type: `javascript/auto`,
         use: [loaders.js(options)],
       }
     }
 
     rules.js = js
   }
 
-  /**
-   * mjs loader:
-   * webpack 4 has issues automatically dealing with
-   * the .mjs extension, thus we need to explicitly
-   * add this rule to use the default webpack js loader
-   */
-  {
-    let mjs = (options = {}) => {
-      return {
-        test: /\.mjs$/,
-        include: /node_modules/,
-        type: `javascript/auto`,
-        ...options,
-      }
-    }
-
-    rules.mjs = mjs
-  }
-
   {
     let eslint = schema => {
       return {

packages/gatsby/src/utils/webpack.config.js

@@ -249,7 +249,6 @@ module.exports = async (program, directory, suppliedStage) => {
     // Common config for every env.
     // prettier-ignore
     let configRules = [
-      rules.mjs(),
       rules.js(),
       rules.yaml(),
       rules.fonts(),