HTMLElement: transitionrun event

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The transitionrun event is fired when a CSS transition is first created, i.e. before any transition-delay has begun.

Bubbles Yes
Cancelable No
Interface TransitionEvent
Event handler property ontransitionrun


This code adds a listener to the transitionrun event:

el.addEventListener('transitionrun', () => {
  console.log('Transition is running but hasn\'t necessarily started transitioning yet');

The same, but using the ontransitionrun property instead of addEventListener():

el.ontransitionrun = () => {
  console.log('Transition started running, and will start transitioning when the transition delay has expired');

Live example

In the following example, we have a simple <div> element, styled with a transition that includes a delay:

<div class="transition">Hover over me</div>
<div class="message"></div>
.transition {
  width: 100px;
  height: 100px;
  background: rgba(255,0,0,1);
  transition-property: transform, background;
  transition-duration: 2s;
  transition-delay: 1s;

.transition:hover {
  transform: rotate(90deg);
  background: rgba(255,0,0,0);

To this, we'll add some JavaScript to indicate where the transitionstart and transitionrun events fire.

const el = document.querySelector('.transition');
const message = document.querySelector('.message');

el.addEventListener('transitionrun', function() {
  message.textContent = 'transitionrun fired';

el.addEventListener('transitionstart', function() {
  message.textContent = 'transitionstart fired';

el.addEventListener('transitionend', function() {
  message.textContent = 'transitionend fired';

The difference is that:

  • transitionrun fires when the transition is created (i.e. at the start of any delay).
  • transitionstart fires when the actual animation has begun (i.e. at the end of any delay).

The transitionrun will occur even if the transition is canceled before the delay expires. If there is no transition delay or if transition-delay is negative, both transitionrun and transitionstart are fired.


Specification Status Comment
CSS Transitions
The definition of 'transitionrun' in that specification.
Working Draft

Browser compatibility

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
transitionrun eventChrome Full support 74Edge Full support ≤79Firefox Full support 53IE ? Opera Full support 62Safari Full support 13.1
Full support 13.1
Full support 12
Disabled From version 12: this feature is behind the Web Animations preference and the CSS Animations via Web Animations preference.
WebView Android Full support 74Chrome Android Full support 74Firefox Android Full support 53Opera Android Full support 53Safari iOS Full support 13.4
Full support 13.4
Full support 12
Disabled From version 12: this feature is behind the Web Animations preference and the CSS Animations via Web Animations preference.
Samsung Internet Android Full support 11.0


Full support
Full support
Compatibility unknown
Compatibility unknown
User must explicitly enable this feature.
User must explicitly enable this feature.

See also