Binding onunload event to prevent loss of entered reply text

Support agents would benefit from the following functionality:
Binding onunload event to prevent loss of entered reply text

It is already implemented eg. in Wordpress CMS - when user enter a text into a field, a flag is set that makes the browser ask user for confirmation before leaving the page.

Example code:

var inputChanged = false;
function navigateAway() {
  if(inputChanged) {
    return 'If you leave this page, the text you have entered will be lost.';
  }
}

$(window).bind('beforeunload', navigateAway);
$(document).delegate(':input', 'change', function(e) { inputChanged = true; });
$(document).delegate('a', 'click', function() { inputChanged = false; });
$(document).delegate('form', 'submit', function() { inputChanged = false; });