Adding Backbone.noConflict() and keeping track of the original root.Backbone.

backbone.js

@@ -9,25 +9,38 @@
   // Initial Setup
   // -------------
 
+  // Save a reference to the global object.
+  var root = this;
+  
+  // Save the previous value of the `Backbone` variable.
+  var previousBackbone = root.Backbone;
+  
   // The top-level namespace. All public Backbone classes and modules will
   // be attached to this. Exported for both CommonJS and the browser.
   var Backbone;
   if (typeof exports !== 'undefined') {
     Backbone = exports;
   } else {
-    Backbone = this.Backbone = {};
+    Backbone = root.Backbone = {};
   }
 
   // Current version of the library. Keep in sync with `package.json`.
   Backbone.VERSION = '0.3.3';
 
   // Require Underscore, if we're on the server, and it's not already present.
-  var _ = this._;
+  var _ = root._;
   if (!_ && (typeof require !== 'undefined')) _ = require('underscore')._;
 
   // For Backbone's purposes, either jQuery or Zepto owns the `$` variable.
-  var $ = this.jQuery || this.Zepto;
+  var $ = root.jQuery || root.Zepto;
 
+  // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
+  // to its previous owner. Returns a reference to this Backbone object.
+  Backbone.noConflict = function() {
+    root.Backbone = previousBackbone;
+    return this;
+  };
+  
   // Turn on `emulateHTTP` to use support legacy HTTP servers. Setting this option will
   // fake `"PUT"` and `"DELETE"` requests via the `_method` parameter and set a
   // `X-Http-Method-Override` header.

test/noconflict.js

@@ -0,0 +1,12 @@
+$(document).ready(function() {
+
+  module("Backbone.noConflict");
+  
+  test('Backbone.noConflict', function() {
+    var noconflictBackbone = Backbone.noConflict();
+    equals(window.Backbone, undefined, 'Returned window.Backbone');
+    window.Backbone = noconflictBackbone;
+    equals(window.Backbone, noconflictBackbone, 'Backbone is still pointing to the original Backbone');
+  });
+
+});

test/test.html

@@ -10,6 +10,7 @@
   <script type="text/javascript" src="vendor/underscore-1.1.5.js"></script>
   <script type="text/javascript" src="../backbone.js"></script>
 
+  <script type="text/javascript" src="noconflict.js"></script>
   <script type="text/javascript" src="events.js"></script>
   <script type="text/javascript" src="model.js"></script>
   <script type="text/javascript" src="collection.js"></script>