JavaScript: How to simulate change event in internet explorer (delegation)

While I agree that it would be better having only one event listener on the whole form instead of many listeners, one for each element, you have to evaluate the costs and benefits of your decision. The benefit of one listener is a reduced memory footprint. The downside is that you have to do such complex code tricks to get around one browser’s incorrect implementation of events, increasing the execution time, misusing event types, registering and unregistering event listeners repeatedly, maybe causing confusion to some users.

Coming back to the benefit, the memory footprint isn’t so big if you just attach the same function as a listener for all the elements. And memory is something that current computers don’t lack.

Even if this doesn’t answer your question, I’d advise you to stop trying to make this work, and instead attach listeners on each form element.

To address your points a bit:

1. Are you sure about that? I’ve tried the basic example from Microsoft’s documentation, and both IE7 and IE8 fire the onchange listener after I click on an option from the dropdown. It even fires when changing the selection with the up/down keys.

2. While it’s true that you can’t easily connect an event on a label to the affected checkbox, why would you want to do that? The change event will be triggered on the checkbox anyway, and you should only care about that one. However, if you must get to the checkbox from an event on a label, then you could do that manually. If the event targets a label, then you know that the label is somehow related to an input. Depending on how you use labels, you could either select the input element nested inside the label, or get the element with the ID found in the for attribute of the label.

3. One way of fixing the checkboxes return the previous value on change bug is to do a this.blur() on focus events on checkboxes.

4. When you say “handler”, you mean the onfocusin event handler, or the changeDelegator? It is normal to see a focusin event fire when reactivating a tab. I don’t know for sure why the event is fired more than once, so I’m just guessing: one might be the focus that the active input receives; the second might be the focus that the document itself receives; I have no idea why a third call happens. I don’t understand what do you mean by “if the checked state actually changed, […] if I clicked the checkbox directly only once”.