JS文字循环轮播

var cars = 50;
            var n =20;
            function start(){
                n--;
                if(n<=0){
                    n=2*cars;
                    $("#set_time").css("padding-left",cars+"px");
                }else{
                  $("#set_time").css("padding-left",n+"px");
                }
                setTimeout(start,10);
            }
            onload=function(){setTimeout(start,1000)};