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`

Examples

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

HTML

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

CSS

.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);
  }
}

JS

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

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

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

applyAnimation.addEventListener('click', () => {
  animation.classList.toggle('active');
  animationEventLog.textContent = '';
  iterationCount = 0;
  let active = animation.classList.contains('active');
  if (active) {
    applyAnimation.textContent = "Cancel animation";
  } else {
    applyAnimation.textContent = "Activate animation";
  }
});

Result

Specifications

Specification
CSS Animations Level 2 (CSS Animations 2) # eventdef-animationevent-animationstart

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`animationstart_event`	43	12	51	10	30	9	43	43	51	30	9	4.0