Get element currently under mouse without using mo

Question

WRT building a Firefox Add-on.

Is it possible to get the element under the mouse via some XPCOM or javascript method? (non-js-ctypes please as that requires OS specificity)

I want to detect what is under the mouse when user presses Ctrl + Shift + M.

Right now I'm adding a mouseover listener to the document when the user presses this hotkey, so I can get the element under the mouse when he moves it, but not the element that was under the mouse exactly when he pressed the hotkey combination.

Answer 1

I just looked through the source for code that gets (or stores and makes available) the cursor position. I didn't find anything one could use (from Javascript, XPCOM or not). I might have missed something... MXR is your friend.

However, if you want to avoid mousemove (and this is a good idea in general), you can just look for the innermost hovered element, e.g. like so.

function getInnermostHovered() {
    var n = document.querySelector(":hover");
    var nn;
    while (n) {
        nn = n;
        n = nn.querySelector(":hover");
    }
    return nn;
}

(fiddle demoing the principle)

While this is what I'd consider a hack, it seems to work good enough most of the time, but will fail if the element has mouse events disabled via pointer-events. There could be other issues I didn't think of...

Of course, this can return nothing when the document has no hovered element (e.g. the mouse is not actually within the document).