Element: transitionstart event

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

This event is not cancelable.

Syntax

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

js
addEventListener("transitionstart", (event) => { })

ontransitionstart = (event) => { }

Event type

A TransitionEvent. Inherits from Event.

EventTransitionEvent

Examples

This code adds a listener to the transitionstart event:

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

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

js
element.ontransitionstart = () => {
  console.log("Started transitioning");
};

Live example

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

html
<div class="transition">Hover over me</div>
<div class="message"></div>
css
.transition {
  width: 100px;
  height: 100px;
  background: red;
  transition-property: transform, background;
  transition-duration: 2s;
  transition-delay: 1s;
}

.transition:hover {
  transform: rotate(90deg);
  background: transparent;
}

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

js
const transition = document.querySelector(".transition");
const message = document.querySelector(".message");

transition.addEventListener("transitionrun", () => {
  message.textContent = "transitionrun fired";
});

transition.addEventListener("transitionstart", () => {
  message.textContent = "transitionstart fired";
});

transition.addEventListener("transitionend", () => {
  message.textContent = "transitionend fired";
});

The difference is that:

Specifications

See also