xplat/js: replace import() calls by require.async() calls

Reviewed By: mjesun

Differential Revision: D6147316

fbshipit-source-id: b93a247ce0830a5db250824d22e81a3b786daf36

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

@@ -33,14 +33,16 @@ export type TransformedCode = {
   map?: ?MappingsMap,
 };
 
+export type Transform<ExtraOptions: {}> = ({|
+  filename: string,
+  localPath: string,
+  options: ExtraOptions & TransformOptions,
+  plugins?: BabelPlugins,
+  src: string,
+|}) => {ast: ?Ast, code: string, map: ?MappingsMap};
+
 export type Transformer<ExtraOptions: {} = {}> = {
-  transform: ({|
-    filename: string,
-    localPath: string,
-    options: ExtraOptions & TransformOptions,
-    plugins?: BabelPlugins,
-    src: string,
-  |}) => {ast: ?Ast, code: string, map: ?MappingsMap},
+  transform: Transform<ExtraOptions>,
   getCacheKey: () => string,
 };
 

packages/metro-bundler/src/transforms/DynamicImports.js

@@ -0,0 +1,29 @@
+/**
+ * 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.
+ */
+
+'use strict';
+
+const template = require('babel-template');
+
+const makeAsyncRequire = template('require.async(ARGS)');
+
+const plugin = {
+  inherits: require('babel-plugin-syntax-dynamic-import'),
+  visitor: {
+    CallExpression(path) {
+      if (path.node.callee.type !== 'Import') {
+        return;
+      }
+      const newImport = makeAsyncRequire({ARGS: path.node.arguments});
+      path.replaceWith(newImport);
+    },
+  },
+};
+
+module.exports = plugin;