判断滚动条是否到达页面的尾部

//取窗口滚动条高度
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;
}

//取窗口可视范围的高度
function getClientHeight()
{
var clientHeight=0;
if(document.body.clientHeight&&document.documentElement.clientHeight)
{
var clientHeight = (document.body.clientHeight<document.documentElement.clientHeight)?document.body.clientHeight:document.documentElement.clientHeight;
}
else
{
var clientHeight = (document.body.clientHeight>document.documentElement.clientHeight)?document.body.clientHeight:document.documentElement.clientHeight;
}
return clientHeight;
}

//取文档内容实际高度
function getScrollHeight()
{
return Math.max(document.body.scrollHeight,document.documentElement.scrollHeight);
}
function test(){
if (getScrollTop()+getClientHeight()==getScrollHeight()){
alert("到达底部");
}else{
alert("没有到达底部");
}
}