Compile code in parallel (#3778)

* Cheap perf gains

* Whoopsie

Author: Timer

packages/react-scripts/config/webpack.config.dev.js

@@ -164,29 +164,45 @@ module.exports = {
           {
             test: /\.(js|jsx|mjs)$/,
             include: paths.appSrc,
-            loader: require.resolve('babel-loader'),
-            options: {
-              // @remove-on-eject-begin
-              babelrc: false,
-              presets: [require.resolve('babel-preset-react-app')],
-              // @remove-on-eject-end
-              // This is a feature of `babel-loader` for webpack (not Babel itself).
-              // It enables caching results in ./node_modules/.cache/babel-loader/
-              // directory for faster rebuilds.
-              cacheDirectory: true,
-            },
+            use: [
+              // This loader parallelizes code compilation, it is optional but
+              // improves compile time on larger projects
+              require.resolve('thread-loader'),
+              {
+                loader: require.resolve('babel-loader'),
+                options: {
+                  // @remove-on-eject-begin
+                  babelrc: false,
+                  presets: [require.resolve('babel-preset-react-app')],
+                  // @remove-on-eject-end
+                  // This is a feature of `babel-loader` for webpack (not Babel itself).
+                  // It enables caching results in ./node_modules/.cache/babel-loader/
+                  // directory for faster rebuilds.
+                  cacheDirectory: true,
+                },
+              },
+            ],
           },
           // Process any JS outside of the app with Babel.
           // Unlike the application JS, we only compile the standard ES features.
           {
             test: /\.js$/,
-            loader: require.resolve('babel-loader'),
-            options: {
-              babelrc: false,
-              compact: false,
-              presets: [require.resolve('babel-preset-react-app/dependencies')],
-              cacheDirectory: true,
-            },
+            use: [
+              // This loader parallelizes code compilation, it is optional but
+              // improves compile time on larger projects
+              require.resolve('thread-loader'),
+              {
+                loader: require.resolve('babel-loader'),
+                options: {
+                  babelrc: false,
+                  compact: false,
+                  presets: [
+                    require.resolve('babel-preset-react-app/dependencies'),
+                  ],
+                  cacheDirectory: true,
+                },
+              },
+            ],
           },
           // "postcss" loader applies autoprefixer to our CSS.
           // "css" loader resolves paths in CSS and adds assets as dependencies.

packages/react-scripts/config/webpack.config.prod.js

@@ -172,26 +172,42 @@ module.exports = {
           {
             test: /\.(js|jsx|mjs)$/,
             include: paths.appSrc,
-            loader: require.resolve('babel-loader'),
-            options: {
-              // @remove-on-eject-begin
-              babelrc: false,
-              presets: [require.resolve('babel-preset-react-app')],
-              // @remove-on-eject-end
-              compact: true,
-            },
+            use: [
+              // This loader parallelizes code compilation, it is optional but
+              // improves compile time on larger projects
+              require.resolve('thread-loader'),
+              {
+                loader: require.resolve('babel-loader'),
+                options: {
+                  // @remove-on-eject-begin
+                  babelrc: false,
+                  presets: [require.resolve('babel-preset-react-app')],
+                  // @remove-on-eject-end
+                  compact: true,
+                },
+              },
+            ],
           },
           // Process any JS outside of the app with Babel.
           // Unlike the application JS, we only compile the standard ES features.
           {
             test: /\.js$/,
-            loader: require.resolve('babel-loader'),
-            options: {
-              babelrc: false,
-              compact: false,
-              presets: [require.resolve('babel-preset-react-app/dependencies')],
-              cacheDirectory: true,
-            },
+            use: [
+              // This loader parallelizes code compilation, it is optional but
+              // improves compile time on larger projects
+              require.resolve('thread-loader'),
+              {
+                loader: require.resolve('babel-loader'),
+                options: {
+                  babelrc: false,
+                  compact: false,
+                  presets: [
+                    require.resolve('babel-preset-react-app/dependencies'),
+                  ],
+                  cacheDirectory: true,
+                },
+              },
+            ],
           },
           // The notation here is somewhat confusing.
           // "postcss" loader applies autoprefixer to our CSS.

packages/react-scripts/package.json

@@ -54,6 +54,7 @@
     "react-dev-utils": "^4.2.1",
     "style-loader": "0.19.0",
     "sw-precache-webpack-plugin": "0.11.4",
+    "thread-loader": "1.1.2",
     "uglifyjs-webpack-plugin": "1.1.6",
     "url-loader": "0.6.2",
     "webpack": "3.8.1",