原生JS实现返回顶部功能

1.无动画版本

window.scrollTo(0,0);  

2.带动画版本

(function smoothscroll(){
    var currentScroll = document.documentElement.scrollTop || document.body.scrollTop;
    if (currentScroll > 0) {
         window.requestAnimationFrame(smoothscroll);
         window.scrollTo (0,currentScroll - (currentScroll/5));
    }
})();