30-seconds-of-code/snippets/passive-scroll-listener-performance.md

title, shortTitle, type, tags, author, cover, excerpt, dateModified

title	shortTitle	type	tags	author	cover	excerpt	dateModified
Tip: Improve scroll listener performance	Improve scroll listener performance	tip	javascript browser event	chalarangelo	chill-surfing	Scroll listeners can easily become a performance bottleneck for your web application. Here's how to fix that.	2023-03-07T05:00:00-04:00

When working with scroll listeners in JavaScript, one can often run into performance issues. This is because scroll listeners are triggered on every single scroll event, which can be quite frequent. Most of the time, such listeners are used for infinite scrolling and lazy loading, meaning that the scroll event won't be intercepted. As such, Event.preventDefault() will not be called, guving us an optimization opportunity.

window.addEventListener('scroll', () => {
  // Do something
  // Can't use `preventDefault` here
}, { passive: true });

As demonstrated in this code snippet, setting the passive option to true will enable certain performance optimizations in the browser. This way, the browser will know that it can safely skip the event queue and execute the scroll listener immediately. The result is a much smoother experience for the user, as the scroll event will be handled immediately, instead of being queued and handled later.