HTMLElement: transitionrun event

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

Examples

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');
};

<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);
}

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.

Specifications

Browser compatibility

See also

• The GlobalEventHandlers.ontransitionrun event handler
• The TransitionEvent interface
• CSS properties: transition, transition-delay, transition-duration, transition-property, transition-timing-function
• Related events: transitionend, transitionstart, transitioncancel
• This event on Document targets: transitionrun
• This event on Window targets: transitionrun