vue回到顶部

  backTop() {
      var top = document.body.scrollTop || document.documentElement.scrollTop;
      this.duration -= 3;
      this.duration = this.duration <= 0 ? 1 : this.duration;
      var speed = top / this.duration;
      document.documentElement.scrollTop -= speed;
      if (top > 0) {
        this.timer = setTimeout(() => {
          this.backTop();
        }, 16);
      } else {
        this.duration = 50;
        clearTimeout(this.timer);
        
      }
    }