Tweak string comparator implementation.

backbone.js

@@ -733,12 +733,13 @@
     sort: function(options) {
       options || (options = {});
       if (!this.comparator) throw new Error('Cannot sort a set without a comparator');
-      if (typeof this.comparator === "string"){
-        var attrName = this.comparator;
-        this.comparator = function(o){
-          return o.get(attrName);
-        };
+
+      // If provided an attribute name, use it to sort the collection.
+      if (_.isString(this.comparator)) {
+        var attr = this.comparator;
+        this.comparator = function(model){ return model.get(attr); };
       }
+
       var boundComparator = _.bind(this.comparator, this);
       if (this.comparator.length === 1) {
         this.models = this.sortBy(boundComparator);

index.html

@@ -1590,33 +1590,30 @@ var book = Library.get(110);
     <p id="Collection-comparator">
       <b class="header">comparator</b><code>collection.comparator</code>
       <br />
-      By default there is no <b>comparator</b> on a collection.
+      By default there is no <b>comparator</b> for a collection.
       If you define a comparator, it will be used to maintain
       the collection in sorted order. This means that as models are added,
       they are inserted at the correct index in <tt>collection.models</tt>.
-      Comparators come in three different forms:
+      A comparator can be defined as a
+      <a href="http://underscorejs.org/#sortBy">sortBy</a>
+      (pass a function that takes a single argument),
+      as a
+      <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/sort">sort</a>
+      (pass a comparator function that expects two arguments),
+      or as a string indicating the attribute to sort by.
+    </p>
+
+    <p>
+      "sortBy" comparator functions take a model and return a numeric or string
+      value by which the model should be ordered relative to others.
+      "sort" comparator functions take two models, and return <tt>-1</tt> if
+      the first model should come before the second, <tt>0</tt> if they are of
+      the same rank and <tt>1</tt> if the first model should come after.
     </p>
-    <ul>
-      <li>
-        A <a href="http://underscorejs.org/#sortBy">sortBy</a> comparator
-        is a function that takes a model parameter and returns a numeric or string
-        value by which the model should be ordered relative to others.
-      </li>
-      <li>
-        A <a href="https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/sort">sort</a>
-        comparator function takes two models, and return <tt>-1</tt> if the first
-        model should come before the second, <tt>0</tt> if they are of the same rank
-        and <tt>1</tt> if the first model should come after.
-      </li>
-      <li>
-        Finally the comparator can also be a <b>string</b> containing the name of the model
-        attribute we wish to sort by.
-      </li>
-    </ul>
 
     <p>
       Note how even though all of the chapters in this example are added backwards,
-      they come out in the proper order thanks to the comparator:
+      they come out in the proper order:
     </p>
 
 <pre class="runnable">
@@ -1634,25 +1631,6 @@ chapters.add(new Chapter({page: 1, title: "The Beginning"}));
 alert(chapters.pluck('title'));
 </pre>
 
-    <p>
-      As no special computation was done on the model attribute, the previous example also works
-      with a comparator string naming the desired sorting attribute:
-    </p>
-
-<pre class="runnable">
-var Chapter  = Backbone.Model;
-var chapters = new Backbone.Collection;
-
-chapters.comparator = "page";
-
-chapters.add(new Chapter({page: 9, title: "The End"}));
-chapters.add(new Chapter({page: 5, title: "The Middle"}));
-chapters.add(new Chapter({page: 1, title: "The Beginning"}));
-
-alert(chapters.pluck('title'));
-
-</pre>    
-
     <p class="warning">
       Collections with a comparator will not automatically re-sort if you
       later change model attributes, so you may wish to call

test/collection.js

@@ -18,7 +18,7 @@ $(document).ready(function() {
 
   }));
 
-  test("new and sort", 9, function() {
+  test("new and sort", 7, function() {
     equal(col.first(), a, "a should be first");
     equal(col.last(), d, "d should be last");
     col.comparator = function(a, b) {
@@ -32,11 +32,15 @@ $(document).ready(function() {
     equal(col.first(), d, "d should be first");
     equal(col.last(), a, "a should be last");
     equal(col.length, 4);
-    // tests with string comparator
-    col.comparator = "label";
-    col.sort();
-    equal(col.first(), a, "a should be first");
-    equal(col.last(), d, "d should be last");
+  });
+
+  test("String comparator.", 1, function() {
+    var collection = new Backbone.Collection([
+      {id: 3},
+      {id: 1},
+      {id: 2}
+    ], {comparator: 'id'});
+    deepEqual(collection.pluck('id'), [1, 2, 3]);
   });
 
   test("new and parse", 3, function() {