#150 enhancement
Morus Walter

Access to event in Form.Element.EventObserver

Reported by Morus Walter | June 10th, 2008 @ 05:09 PM | in 1.7

It would be great if the event that triggered the callback in an Form.EventObserver would be available in the callback.

While there are a lot of use cases where this is unnecessary, there are use cases where one needs to know which form element was acted on.

There used to be a ticket in the rails trac but that was closed without solution (http://dev.rubyonrails.org/ticke...).

After some hacking within prototype I managed to do a Form.EventObserver variant that does the job.

  Form.XEventObserver = Class.create();
  Form.XEventObserver.prototype = Object.extend(new Abstract.EventObserver(), {
    getValue: function() {
      return Form.serialize(this.element);
    onElementEvent: function( event ) {
      var value = this.getValue();
      if (this.lastValue != value) {
	this.callback(this.element, value, event);
        this.lastValue = value;
    registerCallback: function(element) {
      if (element.type) {
        switch (element.type.toLowerCase()) {
          case 'checkbox':
          case 'radio':
            Event.observe(element, 'click', this.onElementEvent.bindAsEventListener(this));
            Event.observe(element, 'change', this.onElementEvent.bindAsEventListener(this));

Changes basically are:

  • use bindAsEventListener instead of bind in registerCallback
  • provide the event as a third parameter of the callback

One issue I did not fix is, that the event object will be a "naked" event object as created by the browser without the extra methods provided by prototype. (I simply didn't care enough to figure out how to change that).

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