Insert element to the before of specific, child by index  @method insertBefore @param {dom.Element} parent @param {dom.Element} child
function insertBefore(parent, child, index) {
            var parentEl = parent.el,
                childEl = child.el;
            if (parentEl !== undefined && childEl !== undefined) {
                if (parentEl.childNodes[index] !== undefined) {
                    parentEl.insertBefore(childEl, parentEl.childNodes[index]);
                } else {
                    parentEl.appendChild(childEl);
                }
            }
        }