简单 下拉刷新 demo

 $(window).scroll(function() {
  totalheight = parseFloat($(window).height()) + parseFloat($(window).scrollTop()+10);
  if ($(document).height() <= totalheight) {}
 });

 示例:
      <script type="text/javascript">
        $(document).ready(function(){
            var range = 50; //距下边界长度/单位px
            var elemt = 500; //插入元素高度/单位px
            var maxnum = 20; //设置加载最多次数
            var num = 1;
            var totalheight = 0;
            var main = $("#content"); //主体元素
            $(window).scroll(function(){
                var srollPos = $(window).scrollTop(); //滚动条距顶部距离(页面超出窗口的高度)
                //console.log("滚动条到顶部的垂直高度: "+$(document).scrollTop());
                //console.log("页面的文档高度 ："+$(document).height());
                //console.log('浏览器的高度：'+$(window).height());
                totalheight = parseFloat($(window).height()) + parseFloat(srollPos);
                if(($(document).height()-range) <= totalheight && num != maxnum) {
                    main.append("<div style='border:1px solid tomato;margin-top:20px;color:#ac"+(num%20)+(num%20)+";height:"+elemt+"' >hello world"+srollPos+"---"+num+"</div>");
                    num++;
                }
            });
        });
    </script>