title: Handling the model-update-server response in Backbone.js
body: <p>The Backbone.js model updates itself - and its views - locally on the page before
  passing the data to the server and checking the server's response, so if the
  server says "sorry charlie that's no good" the page has already shown the data
  as having changed and thus doesn't correctly represent the server-side state of the object.  What's the correct/elegant way to handle this on the Backbone.js side when the server returns an error?</p>