Keyframe Formats
Element.animate()
, KeyframeEffect()
, and KeyframeEffect.setKeyframes()
all accept objects formatted to represent a set of keyframes. There are several options to this format, which are explained below.
Syntax
There are two different ways to format keyframes:
-
An
array
of objects (keyframes) consisting of properties and values to iterate over. This is the canonical format returned by thegetKeyframes()
method.jselement.animate( [ { // from opacity: 0, color: "#fff", }, { // to opacity: 1, color: "#000", }, ], 2000, );
Offsets for each keyframe can be specified by providing an
offset
value.jselement.animate( [{ opacity: 1 }, { opacity: 0.1, offset: 0.7 }, { opacity: 0 }], 2000, );
Note:
offset
values, if provided, must be between 0.0 and 1.0 (inclusive) and arranged in ascending order.It is not necessary to specify an offset for every keyframe. Keyframes without a specified offset will be evenly spaced between adjacent keyframes.
The easing to apply between keyframes can be specified by providing an
easing
value as illustrated below.jselement.animate( [ { opacity: 1, easing: "ease-out" }, { opacity: 0.1, easing: "ease-in" }, { opacity: 0 }, ], 2000, );
In this example, the specified easing only applies from the keyframe where it is specified until the next keyframe. Any
easing
value specified on theoptions
argument, however, applies across a single iteration of the animation — for the entire duration. -
An
object
containing key-value pairs consisting of the property to animate and anarray
of values to iterate over.jselement.animate( { opacity: [0, 1], // [ from, to ] color: ["#fff", "#000"], // [ from, to ] }, 2000, );
Using this format, the number of elements in each array does not need to be equal. The provided values will be spaced out independently.
jselement.animate( { opacity: [0, 1], // offset: 0, 1 backgroundColor: ["red", "yellow", "green"], // offset: 0, 0.5, 1 }, 2000, );
The special keys
offset
,easing
, andcomposite
(described below) may be specified alongside the property values.jselement.animate( { opacity: [0, 0.9, 1], offset: [0, 0.8], // Shorthand for [ 0, 0.8, 1 ] easing: ["ease-in", "ease-out"], }, 2000, );
After generating a suitable set of keyframes from the property value lists, each supplied offset is applied to the corresponding keyframe. If there are insufficient values, or if the list contains
null
values, the keyframes without specified offsets will be evenly spaced as with the array format described above.If there are too few
easing
orcomposite
values, the corresponding list will be repeated as needed.
Implicit to/from keyframes
In newer browser versions, you are able to set a beginning or end state for an animation only (i.e. a single keyframe), and the browser will infer the other end of the animation if it is able to. For example, consider this simple animation — the Keyframe object looks like so:
let rotate360 = [{ transform: "rotate(360deg)" }];
We have only specified the end state of the animation, and the beginning state is implied.
Attributes
Keyframes specify property-value pairs of the CSS properties to be animated. The property names are specified using camel case so for example background-color
becomes backgroundColor
and background-position-x
becomes backgroundPositionX
. Shorthand values such as margin
are also permitted.
Two exceptional CSS properties are:
float
, which must be written ascssFloat
since "float" is a reserved word in JavaScript. It's just for reference here, this will have no effect on animation since "float" is not an animatable CSS property.offset
, which must be written ascssOffset
since "offset" represents the keyframe offset as described below.
The following special attributes may also be specified:
- offset
-
The offset of the keyframe specified as a number between
0.0
and1.0
inclusive ornull
. This is equivalent to specifying start and end states in percentages in CSS stylesheets using@keyframes
. If this value isnull
or missing, the keyframe will be evenly spaced between adjacent keyframes. - easing
-
The easing function used from this keyframe until the next keyframe in the series.
- composite
-
The
KeyframeEffect.composite
operation used to combine the values specified in this keyframe with the underlying value. This will beauto
if the composite operation specified on the effect is being used.