Function getRelativeScrollOffset

src/utils.js:396–413

* Returns the scroll offset of the given element, added with all the scroll offsets of parent elements. * The value is returned in real pixels. * @param {HTMLElement} el * @return {Array} Offsets in the format of [left, top]

(el)

 * @return {Array}             Offsets in the format of [left, top]
 */
function getRelativeScrollOffset(el) {
	let offsetLeft = 0,
		offsetTop = 0,
		winScroller = getWindowScrollingElement();

	if (el) {
		do {
			let elMatrix = matrix(el),
				scaleX = elMatrix.a,
				scaleY = elMatrix.d;

			offsetLeft += el.scrollLeft * scaleX;
			offsetTop += el.scrollTop * scaleY;
		} while (el !== winScroller && (el = el.parentNode));
	}

	return [offsetLeft, offsetTop];
}

/**
 * Returns the index of the object within the given array