js获取页面元素高度,position:absolute不能撑开父元素

当内部为素为绝对定位时，不能把外部元素撑开，我们可以用给父元素设定最小高度的方法来解决这个问题。解决方法如下。

<div style=”position:relative” id=”a1″>

<div style=”position:absolute” id=”a2″>这是内容</div>

</div>

        window.onload = function () {
            var height = getHeight();
            var a3 = document.getElementById("a1");
            a3.style.minHeight = height + 20 + "px";
            console.log(height);
        }
        $(window).resize(function () {
            var height = getHeight();
            var a3 = document.getElementById("a1");
            a3.style.minHeight = height + 20 + "px";
        });
        function getHeight() {
            var height = 0;
            var div = document.getElementById("a2").getBoundingClientRect();
            if (div.height) {
                height = div.height;
            } else {
                height = div.bottom - div.top;
            }
            return height;
        }