自定义的滚动加载事件

//获取滚动条当前的位置 
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; 
};
//获取当前可是范围的高度 
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); 
};

if (getScrollTop() + getClientHeight() == getScrollHeight()) { }