diff --git a/debugger.html b/debugger.html
index 3b905efe..a69424ea 100644
--- a/debugger.html
+++ b/debugger.html
@@ -42,32 +42,28 @@ function setStatus(status) {
   document.getElementById('status').innerHTML = status;
 }
 
+// This worker will run the application javascript code,
+// making sure that it's run in an environment without a global
+// document, to make it consistent with the JSC executor environment.
+var worker = new Worker('debuggerWorker.js');
+
 var messageHandlers = {
   // This method is a bit hacky. Catalyst asks for a new clean JS runtime.
   // The easiest way to do this is to reload this page. That also means that
   // web socket connection will be lost. To send reply back we need to remember
-  // message id
+  // message id.
+  // This message also needs to be handled outside of the worker, since the worker
+  // doesn't have access to local storage.
   'prepareJSRuntime': function(message) {
     window.onbeforeunload = undefined;
     window.localStorage.setItem('sessionID', message.id);
     window.location.reload();
   },
-  'executeApplicationScript': function(message, sendReply) {
-    for (var key in message.inject) {
-      window[key] = JSON.parse(message.inject[key]);
-    }
-    loadScript(message.url, sendReply.bind(null, null));
+  'executeApplicationScript': function(message) {
+    worker.postMessage(message);
   },
-  'executeJSCall': function(message, sendReply) {
-    var returnValue = null;
-    try {
-      if (window && window.require) {
-        var module = window.require(message.moduleName);
-        returnValue = module[message.moduleMethod].apply(module, message.arguments);
-      }
-    } finally {
-      sendReply(JSON.stringify(returnValue));
-    }
+  'executeJSCall': function(message) {
+    worker.postMessage(message);
   }
 };
 
@@ -89,12 +85,9 @@ function connectToDebuggerProxy() {
       return;
     }
 
-    var sendReply = function(result) {
-      ws.send(JSON.stringify({replyID: object.id, result: result}));
-    };
     var handler = messageHandlers[object.method];
     if (handler) {
-      handler(object, sendReply);
+      handler(object);
     } else {
       console.warn('Unknown method: ' + object.method);
     }
@@ -107,18 +100,14 @@ function connectToDebuggerProxy() {
     window.localStorage.removeItem('sessionID');
     debuggerSetTimeout(connectToDebuggerProxy, 100);
   };
+
+  worker.onmessage = function(message) {
+    ws.send(JSON.stringify(message.data));
+  }
 }
 
 connectToDebuggerProxy();
 
-function loadScript(src, callback) {
-  var script = document.createElement('script');
-  script.type = 'text/javascript';
-  script.src = src;
-  script.onload = callback;
-  document.head.appendChild(script);
-}
-
 })();
 </script>
 <style type="text/css">
diff --git a/debuggerWorker.js b/debuggerWorker.js
new file mode 100644
index 00000000..3c3f3136
--- /dev/null
+++ b/debuggerWorker.js
@@ -0,0 +1,46 @@
+/**
+ * Copyright (c) 2015-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.
+ */
+/* global self, importScripts, postMessage, onmessage: true */
+/* eslint no-unused-vars: 0 */
+'use strict';
+
+var messageHandlers = {
+  'executeApplicationScript': function(message, sendReply) {
+    for (var key in message.inject) {
+      self[key] = JSON.parse(message.inject[key]);
+    }
+    importScripts(message.url);
+    sendReply();
+  },
+  'executeJSCall': function(message, sendReply) {
+    var returnValue = [[], [], [], [], []];
+    try {
+      if (require) {
+        returnValue = require(message.moduleName)[message.moduleMethod].apply(null, message.arguments);
+      }
+    } finally {
+      sendReply(JSON.stringify(returnValue));
+    }
+  }
+};
+
+onmessage = function(message) {
+  var object = message.data;
+
+  var sendReply = function(result) {
+    postMessage({replyID: object.id, result: result});
+  };
+
+  var handler = messageHandlers[object.method];
+  if (handler) {
+    handler(object, sendReply);
+  } else {
+    console.warn('Unknown method: ' + object.method);
+  }
+};
diff --git a/packager.js b/packager.js
index d5a41b46..9e5455ea 100644
--- a/packager.js
+++ b/packager.js
@@ -184,6 +184,12 @@ function getDevToolsLauncher(options) {
       var debuggerPath = path.join(__dirname, 'debugger.html');
       res.writeHead(200, {'Content-Type': 'text/html'});
       fs.createReadStream(debuggerPath).pipe(res);
+
+    } else if (req.url === '/debuggerWorker.js') {
+      var workerPath = path.join(__dirname, 'debuggerWorker.js');
+      res.writeHead(200, {'Content-Type': 'application/javascript'});
+      fs.createReadStream(workerPath).pipe(res);
+
     } else if (req.url === '/launch-chrome-devtools') {
       var debuggerURL = 'http://localhost:' + options.port + '/debugger-ui';
       var script = 'launchChromeDevTools.applescript';