Web/API/EffectTiming/iterationStart

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

Web Animations API's EffectTiming dictionary's iterationStart property specifies the repetition number which repetition the animation begins at and its progress through it.

Element.animate(), KeyframeEffectReadOnly.KeyframeEffectReadOnly(), and KeyframeEffect.KeyframeEffect() all accept an object of timing properties including iterationStart. The value of iterationStart corresponds directly to AnimationEffectTimingReadOnly.iterationStart in timing objects returned by AnimationEffectReadOnly, KeyframeEffectReadOnly, and KeyframeEffect.

Syntax

var timingProperties = {
  iterationStart = iterationNumber
};

timingProperties.iterationStart = iterationNumber;

Value

A floating-point value whose value is at least 0 and is not +Infinity, indicating the offset into the number of iterations the animation sequence is to run at which to start animating. iterationStart represents the iteration index at which the animation effect begins as well as its progress through that iteration.

Usually you'll use a value between 0.0 and 1.0 to indicate an offset into the first run of the animation at which to begin the animation performance, but any positive, non-infinite value is allowed. Since all animations' iteration indexes start at 0, a value of 0.5 would start the animation halfway through its first iteration or loop. Meanwhile, a value of 1.2 means the animation will begin playback 20% of the way through its second iteration, and so forth.

It's currently undefined what happens if you specify a value of iterationStart which is greater than the value of AnimationEffectTimingProperties.iterations. See issue 170 in the Web Animations API specification's issue tracker for details and status of any changes to the specification in this regard.

Specifications

Specification	Status	Comment
Web AnimationsThe definition of 'iterationStart' in that specification.	Working Draft	Editor's draft.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`iterationStart` Experimental'	Chrome Full support 52	Edge Full support ≤79	Firefox Full support 63	IE No support No	Opera Full support Yes	Safari No support No	WebView Android Full support 52	Chrome Android Full support 52	Firefox Android Full support 63	Opera Android No support No	Safari iOS No support No	Samsung Internet Android Full support 6.0

Legend

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