原生JS返回顶部动画

AnimatedToTop.html

<div it="gotop"> </div>
<script>
  backTop = function (btnId){
	var btn = document.getElementById(btnId);
	var d = document.documentElement;
	var b = document.body;
	window.onscroll = btnDisplay;
	btn.onclick = function (){
		btn.style.display = "none";
		window.onscroll = null;
		this.timer = setInterval(function(){
			d.scrollTop -= Math.ceil((d.scrollTop+b.scrollTop)*0.1);
			b.scrollTop -= Math.ceil((d.scrollTop+b.scrollTop)*0.1);
			if((d.scrollTop + b.scrollTop) == 0)
				clearInterval(btn.timer,window.onscroll = btnDisplay);
		},10);
	};
	function btnDisplay(){
		btn.style.display=(d.scrollTop+b.scrollTop>200)?'block':"none";
	}
};
backTop('gotop');//返回顶部调用
</script>