Document: scroll event

The scroll event fires when the document view has been scrolled. For element scrolling, see Element: scroll event.

Note: In iOS UIWebViews, scroll events are not fired while scrolling is taking place; they are only fired after the scrolling has completed. See Bootstrap issue #16202. Safari and WKWebViews are not affected by this bug.

Syntax

Use the event name in methods like addEventListener(), or set an event handler property.

addEventListener('scroll', (event) => {});

onscroll = (event) => { };

Event type

A generic Event.

Examples

Scroll event throttling

Since scroll events can fire at a high rate, the event handler shouldn't execute computationally expensive operations such as DOM modifications. Instead, it is recommended to throttle the event using requestAnimationFrame(), setTimeout(), or a CustomEvent, as follows.

Note, however, that input events and animation frames are fired at about the same rate, and therefore the optimization below is often unnecessary. This example optimizes the scroll event for requestAnimationFrame.

let lastKnownScrollPosition = 0;
let ticking = false;

function doSomething(scrollPos) {
  // Do something with the scroll position
}

document.addEventListener('scroll', (e) => {
  lastKnownScrollPosition = window.scrollY;

  if (!ticking) {
    window.requestAnimationFrame(() => {
      doSomething(lastKnownScrollPosition);
      ticking = false;
    });

    ticking = true;
  }
});

See more, similar examples on the resize event page.

Specifications

Specification
CSSOM View Module
# eventdef-document-scroll
HTML Standard
# handler-onscroll

Browser compatibility

BCD tables only load in the browser

See also