title: underscore.js .map method breaks ie8
body: <p>I use backbone.js, this code is works fine all modern browser except internet explorer.  </p>
  
  <pre><code>var posts = postList.map(function(model){ return model.toJSON(); });
  </code></pre>
  
  <p>Something wrong with the toJSON() method, what can I do?</p>
  
  <p><strong>Edit:</strong>  </p>
  
  <pre><code>var posts = postList.map(function(model){ return model });
  </code></pre>
  
  <p>without toJSON(), still not working, maybe the .map method is the guilty?</p>