js控制网页滚动条往下滚动

function aa(i){
    var tm = setInterval(function(){
        var t = $(window).scrollTop();
        var d = i < t ? Math.min((i-t)/10, -1) : Math.max((i-t)/10, 1)
        $(window).scrollTop( t + d );
        if($(window).scrollTop()==i)clearInterval(tm);
    },30)
}