title: Backbonejs Collection URL this.isNew is not a function
body: <p>I am having a problem using this.isNew inside my collection and and it looks something like below:</p>
  
  <pre><code>window.MyModel = Backbone.Model.extend({
      idAttribute: "_id",
  });
  
  window.MyModelList = Backbone.Collection.extend({
      alert('Collection');
      model: MyModel,
      url: function() {
          if (this.isNew()) {
             alert('show all');
             // will ask the server to show all items
             return 'api/site/showall'
      } else {
          alert('create new item');
          // will ask the server to create new item
          return 'api/site/new'
      }
  });
  </code></pre>
  
  <p>It alerts the "Collection" but not the "show all" and "create new item" then I'm getting the error "TypeError:this.isNew is not a function"</p>
  
  <p>Thanks,</p>