Element: animationstart event

The animationstart event is fired when a CSS Animation has started. If there is an animation-delay, this event will fire once the delay period has expired. A negative delay will cause the event to fire with an elapsedTime equal to the absolute value of the delay (and, correspondingly, the animation will begin playing at that time index into the sequence).


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

addEventListener("animationstart", (event) => {});

onanimationstart = (event) => {};

Event type

Event properties

Also inherits properties from its parent Event.

AnimationEvent.animationName Read only

A string containing the value of the animation-name that generated the animation.

AnimationEvent.elapsedTime Read only

A float giving the amount of time the animation has been running, in seconds, when this event fired, excluding any time the animation was paused. For an animationstart event, elapsedTime is 0.0 unless there was a negative value for animation-delay, in which case the event will be fired with elapsedTime containing (-1 * delay).

AnimationEvent.pseudoElement Read only

A string, starting with '::', containing the name of the pseudo-element the animation runs on. If the animation doesn't run on a pseudo-element but on the element, an empty string: ''.


This listens for the animationstart event and logs a message when it is fired:

const animated = document.querySelector(".animated");

animated.addEventListener("animationstart", () => {
  console.log("Animation started");

The same, but using onanimationstart:

const animated = document.querySelector(".animated");

animated.onanimationstart = () => {
  console.log("Animation started");

Live example


<div class="animation-example">
  <div class="container">
    <p class="animation">You chose a cold night to visit our planet.</p>
  <button class="activate" type="button">Activate animation</button>
  <div class="event-log"></div>


.container {
  height: 3rem;

.event-log {
  width: 25rem;
  height: 2rem;
  border: 1px solid black;
  margin: 0.2rem;
  padding: 0.2rem;

.animation.active {
  animation-duration: 2s;
  animation-name: slidein;
  animation-iteration-count: 2;

@keyframes slidein {
  from {
    transform: translateX(100%) scaleX(3);
  to {
    transform: translateX(0) scaleX(1);


const animation = document.querySelector("p.animation");
const animationEventLog = document.querySelector(
const applyAnimation = document.querySelector(
let iterationCount = 0;

animation.addEventListener("animationstart", () => {
  animationEventLog.textContent = `${animationEventLog.textContent}'animation started' `;

animation.addEventListener("animationiteration", () => {
  animationEventLog.textContent = `${animationEventLog.textContent}'animation iterations: ${iterationCount}' `;

animation.addEventListener("animationend", () => {
  animationEventLog.textContent = `${animationEventLog.textContent}'animation ended'`;
  applyAnimation.textContent = "Activate animation";

animation.addEventListener("animationcancel", () => {
  animationEventLog.textContent = `${animationEventLog.textContent}'animation canceled'`;

applyAnimation.addEventListener("click", () => {
  animationEventLog.textContent = "";
  iterationCount = 0;
  const active = animation.classList.contains("active");
  applyAnimation.textContent = active
    ? "Cancel animation"
    : "Activate animation";



CSS Animations Level 1
# eventdef-globaleventhandlers-animationstart

Browser compatibility

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See also