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Why changing animation-direction does not reverse a running animation
CSS animation-direction sets the direction used for an animation’s iterations. Values such as reverse, alternate and alternate-reverse describe how those configured cycles run; changing the property is not the same as telling an existing animation to turn around at its current position. See the MDN reference for animation-direction.
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For declarative effects with a predetermined iteration pattern, CSS remains appropriate. When the direction must change in response to a user action or application state while the effect is underway, use playback control on the animation object instead.
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Reverse an animation created with the Web Animations API
The Web Animations API exposes playback controls—including play, pause, reverse, finish and cancel—through an Animation object. If you created an effect with element.animate(), keep the returned object and call reverse() when the direction should change:
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const animation = element.animate(
[
{ transform: "translateX(0)" },
{ transform: "translateX(100px)" }
],
{ duration: 500, fill: "both" }
);
// Changes direction from the animation's current position.
animation.reverse();reverse() inverts playback direction and continues playback. If the animation is paused, calling it resumes playback in reverse; if it has not yet played, it plays backward. It does not restart the effect from its original endpoint. See MDN’s Animation.reverse() reference.
Reverse a CSS animation already applied to an element
A CSS animation can have an associated Web Animations API Animation object. Retrieve animations associated with the target element using getAnimations(), then choose the specific one to reverse:
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const animations = element.getAnimations();
const animation = animations.find(candidate => /* identify the intended animation */);
if (animation) {
animation.reverse();
}The example deliberately leaves identification to your application: an element can have more than one associated animation, and reversing every returned object may affect unrelated effects. For broader discovery, MDN’s guide to finding animations with Document.getAnimations() explains the document-level method. Inspect the returned objects and target the intended animation rather than applying reversal indiscriminately.
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The Web Animations specification defines reverse playback as a change to the animation’s playback direction. With a negative playback rate, animation time decreases as timeline time advances; the specification describes a playback rate of -1 as decreasing current time at the same rate that the timeline’s time values increase. Read the W3C Web Animations specification.
That is why reversing an active animation can continue from its current position instead of jumping immediately to the opposite endpoint. The animation still depends on its timeline and play state, so the operation is not simply a CSS property swap.
Choose the right control for the job
| Approach | What it controls | Use it when |
|---|---|---|
CSS animation-direction |
Direction for configured animation iterations | The effect’s cycle pattern is known in advance |
Web Animations API reverse() |
Playback direction on a particular Animation object |
Code must change direction during playback |
finish() |
Moves an animation to its endpoint in the current direction | The effect should complete immediately, not turn around |
cancel() |
Aborts playback and clears the effect | The effect should stop, not play in reverse |
The API is imperative: your code must obtain and manage the relevant animation object. CSS is declarative: its properties describe the effect and iteration behavior. The API’s additional control is useful for state changes during playback, but it makes selecting the right animation and accounting for its timeline part of the implementation.
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Handle errors and unexpected behavior
If reverse() throws
Check whether the animation has an associated active timeline. The W3C specification’s reverse procedure throws InvalidStateError if there is no associated timeline or if that timeline is inactive. Consult the specification’s Web Animations procedures when diagnosing timeline-related behavior.
If the wrong effect changes direction
Inspect the objects returned for the element and identify the intended one before calling reverse(). An element may have multiple animations, so treating the result as a single guaranteed effect can cause unintended changes.
If the animation jumps or does not appear to reverse
Confirm that you are calling reverse() on the object associated with the effect you want to control, and consider whether its current play state or timeline allows playback to continue. finish() and cancel() are not alternatives for changing direction: they respectively complete or abort the effect.
Browser availability
MDN labels Animation.reverse() widely available and reports support across browsers since March 2020. That is a broad compatibility summary, not a guarantee for every browser version or a substitute for checking the environments your application supports. See MDN’s compatibility information.
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