js 移动端H5滑到底部时候加载

<script type="text/javascript">
    /**
     * 到底加载
     */
    var flag=1;
    var rgb = 0;
    $(window).bind("scroll", function () {
        if(getScrollHeight() < getDocumentTop() + getWindowHeight() + 250){ //+200是底部，到250留点距离
            //当滚动条到底时,这里是触发内容
            //异步请求数据,局部刷新dom
            pageNum++;
            //ajax_function()
//            if (flag == 1) {
//                flag=0;
//                var temp = `<div style="height:500px; background:rgb(100,${rgb},${rgb});"></div>`;
//                $('body').append(temp);
//                rgb = rgb + 20;
//                flag = 1;
//            }
        }
    });

    //文档高度
    function getDocumentTop() {
        var scrollTop =  0, bodyScrollTop = 0, documentScrollTop = 0;
        if (document.body) {
            bodyScrollTop = document.body.scrollTop;
        }
        if (document.documentElement) {
            documentScrollTop = document.documentElement.scrollTop;
        }
        scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop;
        console.log("scrollTop:"+scrollTop);
        return scrollTop;
    }

    //可视窗口高度
    function getWindowHeight() {
        var windowHeight = 0;
        if (document.compatMode == "CSS1Compat") {
            windowHeight = document.documentElement.clientHeight;
        } else {
            windowHeight = document.body.clientHeight;
        }
        console.log("windowHeight:"+windowHeight);
        return windowHeight;
    }

    //滚动条滚动高度
    function getScrollHeight() {
        var scrollHeight = 0, bodyScrollHeight = 0, documentScrollHeight = 0;
        if (document.body) {
            bodyScrollHeight = document.body.scrollHeight;
        }
        if (document.documentElement) {
            documentScrollHeight = document.documentElement.scrollHeight;
        }
        scrollHeight = (bodyScrollHeight - documentScrollHeight > 0) ? bodyScrollHeight : documentScrollHeight;
        console.log("scrollHeight:"+scrollHeight);
        return scrollHeight;
    }
</script>