Allowing Model#defaults to be a function as well as a hash.

backbone.js

@@ -115,8 +115,12 @@
   // Create a new model, with defined attributes. A client id (`cid`)
   // is automatically generated and assigned for you.
   Backbone.Model = function(attributes, options) {
+    var defaults;
     attributes || (attributes = {});
-    if (this.defaults) attributes = _.extend({}, this.defaults, attributes);
+    if (defaults = this.defaults) {
+      if (_.isFunction(defaults)) defaults = defaults();
+      attributes = _.extend({}, defaults, attributes);
+    }
     this.attributes = {};
     this._escapedAttributes = {};
     this.cid = _.uniqueId('c');

index.html

@@ -642,11 +642,11 @@ if (note.has("title")) {
     </p>
 
     <p id="Model-defaults">
-      <b class="header">defaults</b><code>model.defaults</code>
+      <b class="header">defaults</b><code>model.defaults or model.defaults()</code>
       <br />
-      The <b>defaults</b> hash can be used to specify the default attributes
-      for your model. When creating an instance of the model, any unspecified
-      attributes will be set to their default value.
+      The <b>defaults</b> hash (or function) can be used to specify the default 
+      attributes for your model. When creating an instance of the model, 
+      any unspecified attributes will be set to their default value.
     </p>
 
 <pre class="runnable">

test/model.js

@@ -172,6 +172,17 @@ $(document).ready(function() {
     var model = new Defaulted({two: null});
     equals(model.get('one'), 1);
     equals(model.get('two'), null);
+    Defaulted = Backbone.Model.extend({
+      defaults: function() {
+        return {
+          "one": 3,
+          "two": 4
+        };
+      }
+    });
+    var model = new Defaulted({two: null});
+    equals(model.get('one'), 3);
+    equals(model.get('two'), null);
   });
 
   test("Model: change, hasChanged, changedAttributes, previous, previousAttributes", function() {