title: Change form (create to update) using javascript
body: <p>I have a simple review system where users can select a number of stars and this creates an AJAX call to the <code>create</code> action (if the review is new).</p>
  
  <p>If the review already exists, I want it to instead call the <code>update</code> action.</p>
  
  <p>Right now, if the page loads to a blank review, the first change will call <code>create</code>, but so will all subsequent requests until I completely reload the page.</p>
  
  <p>How can I get <code>create.js.erb</code> to change the reviews form from <code>create</code> to <code>update</code> without refreshing the page?</p>
  
  <h3>Clarification</h3>
  
  <p>If a particular user enters the page for the first time, they should be able to create a review, then edit their own review, without needing to refresh the page. My problem is that the create <b>then</b> update transition isn't happening.</p>