Make "scrollLeft" / "scrollTop" changes not trigger scroll event listener

Question

Currently my program is in a spot where it both listens for the user to scroll a certain element, but also, at times, automatically scrolls this element by itself. (Not a gradual, pretty scroll, but an instant jump. It makes sense in context, I swear.)

Is there a way to make the scroll event not trigger if the scrolling was done by setting scrollLeft or scrollTop? My first thought was a basic switch, like:

ignoreScrollEvents = true; element.scrollLeft = x; ignoreScrollEvents = false;  function onScroll() {   if(ignoreScrollEvents) return false; } 

but since events don't trigger immediately (oops, duhh), that's not a workable solution. What other sort of answers could I try? I'm also using jQuery, if that helps anything.

Answer 1

Easiest generic method? Just reset the flag in the event handler. You'll want to check first if you're actually changing the value, as otherwise an event won't be fired - as Rodrigo notes, a good practice here is to factor this out into so-called "setter" functions:

function setScrollLeft(x) {   if ( element.scrollLeft != x )   {     ignoreScrollEvents = true;     element.scrollLeft = x;   } }   ...  function onScroll()  {   var ignore = ignoreScrollEvents;   ignoreScrollEvents = false;    if (ignore) return false;    ... } 

But, depending on your needs, you may already be storing the scroll position somewhere; if so, just update and check that as your flag. Something like:

element.scrollLeft = currentScrollLeft = x;  ...  function onScroll()  {   // retrieve element, etc...     if (element.scrollLeft == currentScrollLeft) return false;    ... }