如何判断元素是否在当前文档显示区内？

        function getHeight(e){
            var h = 0;
            var obj = e;
            while(obj){
                h += obj.offsetTop;     // 不断累加e元素和其每个父元素的offsetTop
                obj = obj.offsetParent;
            }
            return h;
        }

        function ifInWindow (element) {
            var s = document.body.scrollTop;
            var h1 = window.innerHeight;
            var off = getHeight(element);
            var h2 = element.clientHeight;
            if(s > off - h1 && s < off + h2){
                    return true;
            }
            return false;
        }

        function getHeight(e){
            var h = 0;
            var obj = e;
            while(obj){
                h += obj.offsetTop;     // 不断累加e元素和其每个父元素的offsetTop
                obj = obj.offsetParent;
            }
            return h;
        }