检测滚动方向

可以通过存储先前的scrollTop值并将其与当前scrollTop值进行比较来检测到它。

JS：

var lastScrollTop = 0;// element should be replaced with the actual target element on which you have applied scroll, use window in case of no target element.element.addEventListener("scroll", function(){ // or window.addEventListener("scroll"....   var st = window.pageYOffset || document.documentElement.scrollTop; // Credits: "https://github.com/qeremy/so/blob/master/so.dom.js#L426"   if (st > lastScrollTop){      // downscroll pre   } else {      // upscroll pre   }   lastScrollTop = st <= 0 ? 0 : st; // For Mobile or negative scrolling}, false);