js实现固定时长内，滚动条自动滚动到底部

原版js

    var height = document.body.clientHeight;
    var number = 0;  //控制结束累加器
    var length = 0;  //控制每次翻滚长度
    var frequency = 120;    //控制总时间
    var time = setInterval(function(){
        number += 1;
        if(number == frequency + 1){
            clearInterval(time);
        } else {
            length += height / frequency;
            document.documentElement.scrollTop = length;
        }
    },1000);        //每隔1S翻滚

jQuery

function() {
    test.height = document.body.clientHeight;
    var number = 0;
    var length = 0;
    var time = setInterval(function(){
        number += 1;
        if(number == 121){
            clearInterval(time);
        } else {
            length += test.height / 120;
            $(document).scrollTop(length);  //只有此处有区别
        }
    },1000);
}