判断页面是否滑到底部

// 获取滑动位置
function getScrollTop(){
    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;
    return scrollTop;
}
//文档的总高度
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;
    return scrollHeight;
}
//浏览器视口的高度
function getWindowHeight(){
    var windowHeight = 0;
    if(document.compatMode == 'CSS1Compat'){
        windowHeight = document.documentElement.clientHeight;
    }else{
        windowHeight = document.body.clientHeight;
    }
    return windowHeight;
}

// 判断页面是否滑到底部
 var bottomFlag = (getScrollTop() + getWindowHeight() == getScrollHeight()) ? true : false;