js控制html页面滚动条到底端触发事件

 //文档高度
function getDocumentTop() { 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; } //可视窗口高度 function getWindowHeight() {
var windowHeight = 0;    if (document.compatMode == "CSS1Compat") {    windowHeight = document.documentElement.clientHeight; } else {    windowHeight = document.body.clientHeight; } return windowHeight;
}
//滚动条滚动高度 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; } window.onscroll = function () { //监听事件内容 if(getScrollHeight() == getWindowHeight() + getDocumentTop()){     //当滚动条到底时,这里是触发内容
    //异步请求数据,局部刷新dom
           ajax_function()  } }