原生js返回顶部

let backToTop = function() { ???let scrollToptimer = setInterval(function() { ???????let top = document.body.scrollTop || document.documentElement.scrollTop; ???????let speed = top / 4; ???????if (document.body.scrollTop !== 0) { ???????????document.body.scrollTop -= speed; ???????} else { ???????????document.documentElement.scrollTop -= speed; ???????} ???????if (top === 0) { ???????????clearInterval(scrollToptimer); ???????} ???}, 40);};