Programmatically manipulating DOM element value doesn't fire onchange event

Question

I've got a hidden form field, and when a button gets pressed the value of the hidden field is changed. Now, I've added an observer to the hidden field, listening for changes to occur. For some reason, though, the event listener never kicks in, even though the value of the hidden element changes. I'm using Prototype and Firefox 3.6.

The code looks roughly like this:

button.observe('click', function(event) {
  hiddenField.setValue(someValue);
});

hiddenField.observe('change', function(event) {
  alert('It works!');
});

Does anyone have a clue why the latter observer doesn't execute?

Thanks!

Answer 1

You need event.simulate.js

Fire the event..

button.observe('click', function(event) {
  hiddenField.setValue(someValue);
  hiddenField.simulate('change');
});

And then observe it:

hiddenField.observe('change', function(event) {
  alert('It works!');
});

Answer 2

I don't think input elements that are hidden respond to that event.

I don't know prototype, but I think the events being triggered is entirely up to the browser.

Here is an example with jQuery on JSbin. Notice that changing the text yourself fires the event, however the next part of code that changes the value via script does not fire it.