css - jquery event listen on position changed

Question

I need to listen to an elements relative position. This is particular useful for dynamic layouting issues. There is no option to listen for CSS styles of even position() or offset() attributes.

Why: The relative position can change if a sibling change its dimension inside dialogs or forms (re-layout). So for interactive forms this can help to use i.e. the maximum available height or width of the parent or something like that.

Answer 1

This custom jquery extension listens for object position by timer poll. I.m.o. there is no way to solve this without a timer, because position may be changed without jquery being invoked at all (i.e. re-layouting sibling elements). This solution watches the elements .position() and .offset() values. It can be easily improved to watch .css() styles or other stuff that is not covered by jQuery events.

jQuery extension:

jQuery.fn.onPositionChanged = function (trigger, millis) {
    if (millis == null) millis = 100;
    var o = $(this[0]); // our jquery object
    if (o.length < 1) return o;

    var lastPos = null;
    var lastOff = null;
    setInterval(function () {
        if (o == null || o.length < 1) return o; // abort if element is non existend eny more
        if (lastPos == null) lastPos = o.position();
        if (lastOff == null) lastOff = o.offset();
        var newPos = o.position();
        var newOff = o.offset();
        if (lastPos.top != newPos.top || lastPos.left != newPos.left) {
            $(this).trigger('onPositionChanged', { lastPos: lastPos, newPos: newPos });
            if (typeof (trigger) == "function") trigger(lastPos, newPos);
            lastPos = o.position();
        }
        if (lastOff.top != newOff.top || lastOff.left != newOff.left) {
            $(this).trigger('onOffsetChanged', { lastOff: lastOff, newOff: newOff});
            if (typeof (trigger) == "function") trigger(lastOff, newOff);
            lastOff= o.offset();
        }
    }, millis);

    return o;
};

Call it by:

$("#<SOME_ID>").onPositionChanged(function(){alert("foobar")});