普通的javascript：覆盖对象

Question

There is any object (could be an inline object like but also a block element like or ) as original object.

Now I try to set an overlay over this object, with the same position and size.

=> function overlayObject(originalObject)

Creating the new overlay and mirroring the size of the original object works well. I can also append this new element within the originalObject's parent node.

Regarding the position, left+top for achieving the overlay, is still pending and failing. With original objects that have position:absolute or position:fixed, it's easy, but how to get the exact left/top position to use the same with the overlay ?

Answer 1

You can use offsetTop and offsetLeft to determine the top and left distance of your element to the parent element:

Fiddle

function createOverlay(el) {
    var t = el.offsetTop;
    var l = el.offsetLeft;
    var newEl = el.cloneNode(true);
    newEl.style.margin = "0";
    newEl.style.position = "absolute";
    newEl.style.left = l + "px";
    newEl.style.top = t + "px";
    newEl.style.backgroundColor = "rgba(0,0,255,0.3)";
    el.offestParent.appendChild(newEl);
}