javascript - Detecting scroll direction

Question

So I am trying to use the JavaScript on scroll to call a function. But I wanted to know if I could detect the direction of the the scroll without using jQuery. If not then are there any workarounds?

I was thinking of just putting a 'to top' button but would like to avoid that if I could.

I have now just tried using this code but it didn't work:

if document.body.scrollTop <= 0 {
    alert ("scrolling down")
} else {
    alert ("scrolling up")
}

Answer 1

It can be detected by storing the previous scrollTop value and comparing the current scrollTop value with it.

JavaScript :

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 code
   } else {
      // upscroll code
   }
   lastScrollTop = st <= 0 ? 0 : st; // For Mobile or negative scrolling
}, false);