[ReactNative] Support loading sourcemaps from sourceMappingURL

Libraries/JavaScriptAppEngine/Initialization/loadSourceMap.js

@@ -2,23 +2,42 @@
  * Copyright 2004-present Facebook. All Rights Reserved.
  *
  * @providesModule loadSourceMap
+ * @flow
  */
 
 'use strict';
 
+var Promise = require('Promise');
+var RCTSourceCode = require('NativeModules').RCTSourceCode;
 var SourceMapConsumer = require('SourceMap').SourceMapConsumer;
+var SourceMapURL = require('./source-map-url');
 
-var sourceMapInstance;
+var fetch = require('fetch');
 
-function loadSourceMap() {
-  if (sourceMapInstance !== undefined) {
-    return sourceMapInstance;
+function loadSourceMap(): Promise {
+  return fetchSourceMap()
+    .then(map => new SourceMapConsumer(map));
+}
+
+function fetchSourceMap(): Promise {
+  if (global.RAW_SOURCE_MAP) {
+    return Promise.resolve(global.RAW_SOURCE_MAP);
   }
-  if (!global.RAW_SOURCE_MAP) {
-    return null;
+
+  if (!RCTSourceCode) {
+    return Promise.reject(new Error('RCTSourceCode module is not available'));
   }
-  sourceMapInstance = new SourceMapConsumer(global.RAW_SOURCE_MAP);
-  return sourceMapInstance;
+
+  return new Promise(RCTSourceCode.getScriptText)
+    .then(extractSourceMapURL)
+    .then(fetch)
+    .then(response => response.text())
+}
+
+function extractSourceMapURL({url, text}): string {
+  var mapURL = SourceMapURL.getFrom(text);
+  var baseURL = url.match(/(.+:\/\/.*?)\//)[1];
+  return baseURL + mapURL;
 }
 
 module.exports = loadSourceMap;