web api event

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.

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

ontransitionstart = (event) => { }

Event type

A TransitionEvent. Inherits from Event.

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.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:

<div class="transition">Hover over me</div>
<div class="message"></div>

.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.

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";
});

Interactive exampleOpen the canonical MDN source to run this embedded demo.

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

SpecificationsStandards references are available on the canonical MDN page.

Browser compatibility

Browser compatibilityCompatibility data is available on the canonical MDN page.