JS滚动顶部

function goTop(acceleration, time) {
  acceleration = acceleration || 0.1;//加速度 acceleration
   time = time || 15;//时间间隔
var x=0,y=0;

if (document.documentElement) {
   x = document.documentElement.scrollLeft|| 0;
   y = document.documentElement.scrollTop || 0;
}

var speed = 1 + acceleration;//滚动速度
      //  floor()返回值为小于等于其数值参数的最大整数值 假如 y=36 speed=1.1   36/1.1=32;
      // scrollTo()滚动条将要移动到x y 经过计算得出的值
window.scrollTo(Math.floor(x / speed), Math.floor(y / speed));
    //如果 x (scrollLeft!=0)||y(scrollTop!=0)还未移动到顶部.所以setTimeout()继续执行该函数
    if(x > 0 || y > 0) {
           var invokeFunction = "goTop(" + acceleration + ", " + time + ")";
           window.setTimeout(invokeFunction, time);
      }
}