This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The KeyframeEffect() constructor of the Web Animations API returns a new KeyframeEffect object instance, and also allows you to clone an existing keyframe effect object instance.


var keyframes = new KeyframeEffect(element, keyframeSet, keyframeOptions);
var keyframes = new KeyframeEffect(sourceKeyFrames);


The first type of constructor (see above) creates a completely new KeyframeEffect object instance. Its parameters are:

The DOM element to be animated, or null.
An keyframe object or null.
keyframeOptions Optional

Either an integer representing the animation's duration (in milliseconds), or an Object containing one or more of the following:

delay Optional
The number of milliseconds to delay the start of the animation. Defaults to 0.
direction Optional
Whether the animation runs forwards (normal), backwards (reverse), switches direction after each iteration (alternate), or runs backwards and switches direction after each iteration (alternate-reverse). Defaults to "normal".
duration Optional
The number of milliseconds each iteration of the animation takes to complete. Defaults to 0. Although this is technically optional, keep in mind that your animation will not run if this value is 0.
easing Optional
The rate of the animation's change over time. Accepts the pre-defined values "linear", "ease", "ease-in", "ease-out", and "ease-in-out", or a custom "cubic-bezier" value like "cubic-bezier(0.42, 0, 0.58, 1)". Defaults to "linear".
endDelay Optional
The number of milliseconds to delay after the end of an animation. This is primarily of use when sequencing animations based on the end time of another animation. Defaults to 0. 
fill Optional
Dictates whether the animation's effects should be reflected by the element(s) prior to playing ("backwards"), retained after the animation has completed playing ("forwards"), or both. Defaults to "none".
iterationStart Optional
Describes at what point in the iteration the animation should start. 0.5 would indicate starting halfway through the first iteration for example, and with this value set, an animation with 2 iterations would end halfway through a third iteration. Defaults to 0.0.
iterations Optional
The number of times the animation should repeat. Defaults to 1, and can also take a value of Infinity to make it repeat for as long as the element exists.
Determines how values are combined between this animation and the element's underlying values.
Determines how values build from iteration to iteration in the current animation.

The second type of constructor (see above) creates a clone of an existing  KeyframeEffect object instance. Its parameter is as follows:

A KeyframeEffect object that you want to clone.


In the Follow the White Rabbit example, the KeyframeEffect constructor is used to create a set of keyframes that dictate how the White Rabbit should animate down the hole:

 var rabbitDownKeyframes = new KeyframeEffect( 
    whiteRabbit, // element to animate
      { transform: 'translateY(0%)' }, // keyframe 
      { transform: 'translateY(100%)' } // keyframe
    { duration: 3000, fill: 'forwards' } // keyframe options


Specification Status Comment
Web Animations Level 2
The definition of 'KeyframeEffectOptions.iterationComposite' in that specification.
Draft Added the iterationComposite option.
Web Animations
The definition of 'keyframeEffect()' in that specification.
Working Draft Editor's draft.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
KeyframeEffect() constructor
Chrome Full support YesEdge Full support ≤79Firefox Full support 63IE No support NoOpera No support NoSafari No support NoWebView Android Full support YesChrome Android Full support YesFirefox Android Full support 63Opera Android No support NoSafari iOS No support NoSamsung Internet Android Full support Yes


Full support  
Full support
No support  
No support
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.

See also