Unique element ID, even if element doesn't have one

Question

I'm writing a GreaseMonkey script where I'm iterating through a bunch of elements. For each element, I need a string ID that I can use to reference that element later. The element itself doesn't have an id attribute, and I can't modify the original document to give it one (although I can make DOM changes in my script). I can't store the references in my script because when I need them, the GreaseMonkey script itself will have gone out of scope. Is there some way to get at an "internal" ID that the browser uses, for example? A Firefox-only solution is fine; a cross-browser solution that could be applied in other scenarios would be awesome.

Edit:

• If the GreaseMonkey script is out of scope, how are you referencing the elements later? They GreaseMonkey script is adding events to DOM objects. I can't store the references in an array or some other similar mechanism because when the event fires, the array will be gone because the GreaseMonkey script will have gone out of scope. So the event needs some way to know about the element reference that the script had when the event was attached. And the element in question is not the one to which it is attached.

• Can't you just use a custom property on the element? Yes, but the problem is on the lookup. I'd have to resort to iterating through all the elements looking for the one that has that custom property set to the desired id. That would work, sure, but in large documents it could be very time consuming. I'm looking for something where the browser can do the lookup grunt work.

• Wait, can you or can you not modify the document? I can't modify the source document, but I can make DOM changes in the script. I'll clarify in the question.

• Can you not use closures? Closuses did turn out to work, although I initially thought they wouldn't. See my later post.

It sounds like the answer to the question: "Is there some internal browser ID I could use?" is "No."

Answer 1

The answer is no, there isn't an internal id you can access. Opera and IE (maybe Safari?) support .sourceIndex (which changes if DOM does) but Firefox has nothing of this sort.

You can simulate source-index by generating Xpath to a given node or finding the index of the node from document.getElementsByTagName('*') which will always return elements in source order.

All of this requires a completely static file of course. Changes to DOM will break the lookup.

What I don't understand is how you can loose references to nodes but not to (theoretical) internal id's? Either closures and assignments work or they don't. Or am I missing something?