缓慢回滚置顶动画效果

    this.toTop = () =>{
        let timer = null;
        cancelAnimationFrame(timer);
        timer = requestAnimationFrame(function fn(){
            let oTop = document.body.scrollTop || document.documentElement.scrollTop;
            if(oTop > 0){
                document.body.scrollTop = document.documentElement.scrollTop = oTop - 100;
                timer = requestAnimationFrame(fn);
            }else{
                cancelAnimationFrame(timer);
            }
        });
    };