title: Is it possible to get the index you're sorting over in Underscore.js?
body: <p>I'm using the JS library <a href="http://underscorejs.org" rel="noreferrer">Underscore</a> and in particular using the <strong><a href="http://underscorejs.org/#each" rel="noreferrer"><code>_.each</code></a></strong> and <strong><a href="http://underscorejs.org/#sortBy" rel="noreferrer"><code>_.sortby</code></a></strong> library calls.  I'm wondering if there's any possible way to get the index of the value within the iterator delegate</p>
  
  <pre><code>_.sortBy([1, 4, 2, 66, 444, 9], function(num){ 
      /*It'd be great to have access to the index in here */
      return Math.sin(num); 
  });
  </code></pre>