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;
}
//文件的總高度
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;
}
function getWindowHeight(){
    var windowHeight = 0;
    if(document.compatMode == "CSS1Compat"){
        windowHeight = document
 
.documentElement.clientHeight;
    }else{
        windowHeight = document.body.clientHeight;
    }
    return windowHeight;
}
window.onscroll = function(){
    if(getScrollTop() == 0){
        console.log('頂部')
    }
    if(getScrollTop() + getWindowHeight() == getScrollHeight()){
        console.log("已經到最底部了！!");
    }
};