HTMLElement: transitionstart event

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

The transitionstart event is fired when a CSS transition has actually started, i.e., after any transition-delay has ended.

Bubbles Yes
Cancelable No
Interface TransitionEvent
Event handler property ontransitionstart

Examples

This code adds a listener to the transitionstart event:

element.addEventListener('transitionstart', () => {
  console.log('Started transitioning');
});

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

element.ontransitionrun = () => {
  console.log('Started transitioning');
};

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

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

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

transition.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).

Specifications

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

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
transitionstart 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
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
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

Legend

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

See also