Adds support for web workers

This adds initial support for Web Workers; at least to add basic
modules. Not as much work as you would think, most places where it
checks if we are in a browser will work in a Worker as well. Fixes #201

Author: matthewp

lib/loader.js

@@ -1048,7 +1048,8 @@ function logloads(loads) {
       var traceur;
       Loader.prototype.parse = function(load) {
         if (!traceur) {
-          if (typeof window == 'undefined')
+          if (typeof window == 'undefined' &&
+             typeof WorkerGlobalScope == 'undefined')
             traceur = require('traceur');
           else if (__global.traceur)
             traceur = __global.traceur;

lib/system.js

@@ -12,7 +12,8 @@
 
 (function (global) {
 
-  var isBrowser = typeof window != 'undefined';
+  var isWorker = typeof self !== 'undefined' && typeof WorkerGlobalScope !== 'undefined' && self instanceof WorkerGlobalScope;
+  var isBrowser = typeof window != 'undefined' && !isWorker;
   var Loader = global.Reflect && global.Reflect.Loader || require('./loader');
   var Promise = global.Promise || require('when/es6-shim/Promise');
 
@@ -59,7 +60,7 @@
   }
 
   var fetchTextFromURL;
-  if (isBrowser) {
+  if (isBrowser || isWorker) {
     fetchTextFromURL = function(url, fulfill, reject) {
       var xhr = new XMLHttpRequest();
       var sameDomain = true;
@@ -112,7 +113,7 @@
   }
 
   var System = new Loader({
-    global: isBrowser ? window : global,
+    global: isBrowser ? window : (isWorker ? self : global),
     strict: true,
     normalize: function(name, parentName, parentAddress) {
       if (typeof name != 'string')
@@ -204,7 +205,7 @@
       // according to https://github.com/jorendorff/js-loaders/blob/master/browser-loader.js#L238
       // we should encode everything, but it breaks for servers that don't expect it 
       // like in (https://github.com/systemjs/systemjs/issues/168)
-      if (isBrowser)
+      if (isBrowser || isWorker)
         outPath = outPath.replace(/#/g, '%40');
 
       return toAbsoluteURL(this.baseURL, outPath);
@@ -219,8 +220,8 @@
     },
   });
 
-  if (isBrowser) {
-    var href = window.location.href.split('#')[0].split('?')[0];
+  if (isBrowser || isWorker) {
+    var href = global.location.href.split('#')[0].split('?')[0];
     System.baseURL = href.substring(0, href.lastIndexOf('/') + 1);
   }
   else {

test/test.js

@@ -566,4 +566,12 @@ function runTests() {
   test('System instanceof Loader', function(assert) {
     assert(System instanceof Reflect.Loader, true);
   });
+
+  test('Loading inside of a Web Worker', function(assert) {
+    var worker = new Worker('worker/worker.js');
+
+    worker.onmessage = function(e) {
+      assert(e.data, 'p');
+    };
+  });
 }

test/worker/es6.js

@@ -0,0 +1 @@
+export var p = 'p';

test/worker/worker.js

@@ -0,0 +1,10 @@
+importScripts("../../node_modules/traceur/bin/traceur.js",
+             "../../node_modules/when/es6-shim/Promise.js",
+             "../../lib/loader.js",
+             "../../lib/system.js");
+
+System['import']('es6').then(function(m) {
+  postMessage(m.p);
+}, function(err) {
+  console.error(err, err.stack);
+});