//滑动
function getScrollTop()
{
 var scrollTop = 0;
 if (document.documentElement && document.documentElement.scrollTop) {
   scrollTop = document.documentElement.scrollTop;
  }else if (document.body) {
  scrollTop = document.body.scrollTop;
  }
  return scrollTop;
}
//获取当前可视范围的高度
function getClientHeight()
{
 var clientHeight = 0;
 if (document.body.clientHeight && document.documentElement.clientHeight) {
   clientHeight = Math.min(document.body.clientHeight, document.documentElement.clientHeight);
 }else {
   clientHeight = Math.max(document.body.clientHeight, document.documentElement.clientHeight);
 }
   return clientHeight;
}
//获取文档完整的高度
function getScrollHeight()
{
   return Math.max(document.body.scrollHeight, document.documentElement.scrollHeight);
}
//绑定事件
window.onscroll = function ()
{
 if (getScrollTop() + getClientHeight() == getScrollHeight()) {
  //dosomething
 }
}