title: Invoking an action before the back button is honored?
body: <p>I am adding HTML5 history support to my application.</p>
  
  <p>I'd like to invoke <code>history.replaceState()</code> every time the form is modified so that when the user navigates away and back the form looks just like the user left it.</p>
  
  <p>Unfortunately, it looks like hitting the back button does not trigger <code>onblur</code> and <code>popstate</code> is only invoked after the browser has honored the back button (at which point it is too late to save the form). What event can I listen to that will get triggered <strong>after</strong> the user hits the back button but <strong>before</strong> it is honored?</p>