packager: optimize assets' JS

Reviewed By: davidaurelio

Differential Revision: D5010186

fbshipit-source-id: 3c26d8b8792df1dbc24e5200f28f63e017cb0173

packages/metro-bundler/src/JSTransformer/worker/JsMinification.js

@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) 2016-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+'use strict';
+
+const UGLIFY_JS_OUTPUT_OPTIONS = {
+  ascii_only: true,
+  screw_ie8: true,
+};
+
+module.exports = {UGLIFY_JS_OUTPUT_OPTIONS};

packages/metro-bundler/src/JSTransformer/worker/minify.js

@@ -13,15 +13,14 @@
 
 const uglify = require('uglify-js');
 
+const {UGLIFY_JS_OUTPUT_OPTIONS} = require('./JsMinification');
+
 function minify(filename: string, code: string, sourceMap: ?string) {
   const minifyResult = uglify.minify(code, {
     fromString: true,
     inSourceMap: sourceMap,
     outSourceMap: true,
-    output: {
-      ascii_only: true,
-      screw_ie8: true,
-    },
+    output: UGLIFY_JS_OUTPUT_OPTIONS,
   });
 
   minifyResult.map = JSON.parse(minifyResult.map);

packages/metro-bundler/src/ModuleGraph/types.flow.js

@@ -152,6 +152,7 @@ export type TransformedSourceFile =
 
 export type LibraryOptions = {|
   dependencies?: Array<string>,
+  optimize: boolean,
   platform?: string,
   rebasePath: string => string,
 |};