JS onchange hack for input[type=hidden]

autocomplete_select.js

// make sure you call field.fire('hidden:change') when a hidden field changes
document.observe('dom:loaded', function() {
  $$('input[type=hidden]').each(function(e) {
    var onchange = e.getAttribute('onchange')
    if (onchange) {
      if (typeof(onchange) != 'function') {
        eval("onchange = (function(event){(function(){" + onchange + "}).bind(Event.element(event))()});");
      }
      e.observe('hidden:change', onchange);
    }
  });
})