AJAX needs an observer pattern

Certain things are useful, and AJAX controls most definately couldwill benefit from it.

The idea behind the observer pattern is something you're already familar with: onchange="foo()". However, things get messy when you have to observe the state of a hidden control updated by javascript.

Since I don't have access to the javascript that does the modifying of the hidden control, I need to be able to add an EventListener for modifications of the value via javascript.

//Wonderful psuedocode
var inputA = new Input();
var inputB = new Input();

inputB.value = &inputA.value;
inputA.value = foo;

Or

//Wonderful psuedocode
var inputA = new Input();
var inputB = new Input();

inputA.addEventListener('observerNotify',function() { inputB.value = inputA.value; }, false);

Since I don't have this at the moment, cross browser, it hampers invisibly updating controls and different parts of the UI...