HTMLElement: 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).

Bubbles Yes
Cancelable No
Interface AnimationEvent
Event handler property onanimationstart


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-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('.animation-example>.event-log');
const applyAnimation = document.querySelector('.animation-example>button.activate');
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;
  let active = animation.classList.contains('active');
  if (active) {
    applyAnimation.textContent = "Cancel animation";
  } else {
    applyAnimation.textContent = "Activate animation";



Specification Status Comment
CSS Animations Working Draft Initial definition

Browser compatibility

ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
animationstart eventChrome Full support 43Edge Full support 12Firefox Full support 51IE Full support 10Opera Full support 30Safari Full support 9WebView Android Full support 43Chrome Android Full support 43Firefox Android Full support 51Opera Android Full support 30Safari iOS Full support 9Samsung Internet Android Full support 4.0


Full support
Full support

See also