why not use mouseup event target rather than position for "old school" drag-n-drop?

Question

So, from what I've seen nearly all the IE compatible drag-n-drop use positioning to determine where something is dropped. Doing something like mousedown, determine the position of all droppable, mouseup determine if we are in a droppable position. Why? I made a quick prototype, and it seems to work, which uses the event.target on mouseup (in jquery, so whatever that translates to elsewhere) to determine the drop element.

Is there a compelling reason not to do this? (use the e.target on mouseup). So, mousedown determines what is being dragged, and mouseup determines where it is dropped. Add some variable to make sure we're dragging, and remember what is dragged.

Answer 1

My guess: Because e.target on mouseup can refer to the element you're dragging (or its drag-ghost). If you drag an element, and it (or a translucent ghost-element) follows your cursor like when dragging a file on your desktop, your mouse will always be over the element you're dragging, when you mouse-up.

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Alternatively, if there's no cursor-following, and no ghosting, e.target might refer to an element inside the "dropzone element" and not the dropzone itself.

For instance:

<div id="dropzone_element">
    <div id="previously_dropped_element" />
<div>

<div id="draggable_element" />

So if you drag the draggable element over the dropzone element and release the mouse, you're actually releasing the mouse over the previously dropped element inside the dropzone; not the dropzone itself.

In both cases, checking the mouse position is the only way to get the proper dropzone element.

Those would be my guesses, but I don't have IE to check the actual behavior.

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Edit: In the 1st case position-checking is the only way. In the 2nd case, you could also check the target's ancestors to find the dropzone element, as pointed out by aephus in the comments. If, that is, the previously dropped element has actually be inserted into the dropzone's hierarchy, and not just been positioned to look like it is - although that would be a really weird thing to do :)