title: how to listen for returned json object with jquery
body: <p>I have a page with a form that has a file upload input item targeted to a hidden iframe.  When the form is posted to the iframe the server processes the file and returns a json object.  I'm not sure how to use jquery, or plain old javascript for that matter, to listen for the returned object.  I have some code set up for my iframe such as...</p>
  
  <pre><code>$("#upload_target").load(function () {
     //what to do here - how do I get the json object?
  });
  </code></pre>
  
  <p>Does anyone know how to wire up jquery to listen for the json object that's sent back to the iframe?  Thanks.</p>