getBoundingClientRect

getBoundingClientRect.js

function getElementLeft(elem) {
	var left = elem.offsetLeft,
		current = elem.offsetParent;

	while (current) {
		left += current.offsetLeft;
		current = current.offsetParent;
	}

	return left;
}

function getElementTop(elem) {
	var top = elem.offsetTop,
		current = elem.offsetParent;

	while (current) {
		top += current.offsetTop;
		current = current.offsetParent;
	}

	return top;
}

function getBoundingClientRect(elem) {
	var scrollTop = document.documentElement.scrollTop + document.body.scrollTop,
		scrollLeft = document.documentElement.scrollLeft + document.body.scrollLeft;

	if (document.getBoundingClientRect) {
		if (typeof arguments.callee.offset !== "number") {
			var temp = document.createElement("div");

			temp.style.cssText = "position: absolute; top: 0; left: 0;";
			document.body.appendChild(temp);
			arguments.callee.offset = -temp.getBoundingClientRect().top - scrollTop;

			document.body.removeChild(temp);
			temp = null;
		}

		var rect = elem.getBoundingClientRect(),
			offset = arguments.callee.offset;

		return {
			left: rect.left + offset,
			right: rect.right + offset,
			top: rect.top + offset,
			bottom: rect.bottom + offset
		};
	} else {
		var offsetLeft = getElementLeft(elem),
			offsetTop = getElementTop(elem);

		return {
			left: offsetLeft - scrollLeft,
			right: offsetLeft - scrollLeft + elem.offsetWidth,
			top: offsetTop - scrollTop,
			bottom: offsetTop - scrollTop + elem.offsetHeight
		};
	}
}