Animation

Web animations web-animations

Baseline: Widely available on the web, in every major browser since Sep 2020, and long enough to count on (since Mar 2023).

niso: Partial 91%. 3301 of 3589 subtests pass, by system: Linux 91%, macOS 91%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · Animation, AnimationEffect, AnimationPlaybackEvent, AnimationTimeline

Animation is an interface in idl/web-animations.webidl, inheriting EventTarget, exposed in Window. What it does is on MDN; this page says what niso has of it.

The ready and finished promises cross as (generation, state) pairs: the glue makes a promise per generation and settles it when the hook reports that generation settled.

Status

The web features its members belong to, each with its Baseline status on the web and how much of the feature’s WPT suite passes in niso (see Web platform support).

Feature	On the web	In niso	Members
Web animations	Widely available	Partial 91% 3301 of 3589 subtests pass	24

Members

constructor

constructor

[NisoGlue] constructor(optional AnimationEffect? effect = null, optional AnimationTimeline? timeline);

id

attribute

attribute DOMString id;

int32_t niso_animation_get_id(niso_dom* dom, niso_handle self, niso_str* out);
int32_t niso_animation_set_id(niso_dom* dom, niso_handle self, const char* value, size_t value_len);

effect

attribute

attribute AnimationEffect? effect;

int32_t niso_animation_get_effect(niso_dom* dom, niso_handle self, niso_handle* out);
int32_t niso_animation_set_effect(niso_dom* dom, niso_handle self, niso_handle value);

timeline

attribute

attribute AnimationTimeline? timeline;

int32_t niso_animation_get_timeline(niso_dom* dom, niso_handle self, niso_handle* out);
int32_t niso_animation_set_timeline(niso_dom* dom, niso_handle self, niso_handle value);

startTime

attribute

[NisoGlue] attribute double? startTime;

currentTime

attribute

[NisoGlue] attribute double? currentTime;

playbackRate

attribute

attribute double playbackRate;

int32_t niso_animation_get_playback_rate(niso_dom* dom, niso_handle self, double* out);
int32_t niso_animation_set_playback_rate(niso_dom* dom, niso_handle self, double value);

playState

attribute

readonly attribute AnimationPlayState playState;

int32_t niso_animation_get_play_state(niso_dom* dom, niso_handle self, niso_str* out);

replaceState

attribute

readonly attribute AnimationReplaceState replaceState;

int32_t niso_animation_get_replace_state(niso_dom* dom, niso_handle self, niso_str* out);

pending

attribute

readonly attribute boolean pending;

int32_t niso_animation_get_pending(niso_dom* dom, niso_handle self, bool* out);

ready

attribute

[NisoGlue] readonly attribute Promise<Animation> ready;

finished

attribute

[NisoGlue] readonly attribute Promise<Animation> finished;

onfinish

attribute

attribute EventHandler onfinish;

int32_t niso_animation_get_onfinish(niso_dom* dom, niso_handle self, void** out);
int32_t niso_animation_set_onfinish(niso_dom* dom, niso_handle self, niso_event_handler_non_null_fn value_fn, void* value_userdata, niso_drop_fn value_drop);

oncancel

attribute

attribute EventHandler oncancel;

int32_t niso_animation_get_oncancel(niso_dom* dom, niso_handle self, void** out);
int32_t niso_animation_set_oncancel(niso_dom* dom, niso_handle self, niso_event_handler_non_null_fn value_fn, void* value_userdata, niso_drop_fn value_drop);

onremove

attribute

attribute EventHandler onremove;

int32_t niso_animation_get_onremove(niso_dom* dom, niso_handle self, void** out);
int32_t niso_animation_set_onremove(niso_dom* dom, niso_handle self, niso_event_handler_non_null_fn value_fn, void* value_userdata, niso_drop_fn value_drop);

cancel()

operation

undefined cancel();

int32_t niso_animation_cancel(niso_dom* dom, niso_handle self);

finish()

operation

undefined finish();

int32_t niso_animation_finish(niso_dom* dom, niso_handle self);

play()

operation

undefined play();

int32_t niso_animation_play(niso_dom* dom, niso_handle self);

pause()

operation

undefined pause();

int32_t niso_animation_pause(niso_dom* dom, niso_handle self);

updatePlaybackRate()

operation

undefined updatePlaybackRate(double playbackRate);

int32_t niso_animation_update_playback_rate(niso_dom* dom, niso_handle self, double playback_rate);

reverse()

operation

undefined reverse();

int32_t niso_animation_reverse(niso_dom* dom, niso_handle self);

persist()

operation

undefined persist();

int32_t niso_animation_persist(niso_dom* dom, niso_handle self);

commitStyles()

operation

[CEReactions] undefined commitStyles();

int32_t niso_animation_commit_styles(niso_dom* dom, niso_handle self);

create()

static operation not in JS

[NisoInternal] static Animation create(AnimationEffect? effect, AnimationTimeline? timeline, boolean defaultTimeline);

int32_t niso_animation_create(niso_dom* dom, niso_handle effect, niso_handle timeline, bool default_timeline, niso_handle* out);

startTimeValue()

operation not in JS

[NisoInternal] unrestricted double startTimeValue();

int32_t niso_animation_start_time_value(niso_dom* dom, niso_handle self, double* out);

setStartTimeValue()

operation not in JS

[NisoInternal] undefined setStartTimeValue(unrestricted double time);

int32_t niso_animation_set_start_time_value(niso_dom* dom, niso_handle self, double time);

currentTimeValue()

operation not in JS

[NisoInternal] unrestricted double currentTimeValue();

int32_t niso_animation_current_time_value(niso_dom* dom, niso_handle self, double* out);

setCurrentTimeValue()

operation not in JS

[NisoInternal] undefined setCurrentTimeValue(unrestricted double time);

int32_t niso_animation_set_current_time_value(niso_dom* dom, niso_handle self, double time);

promiseState()

operation not in JS

[NisoInternal] unsigned long promiseState(boolean finished);

int32_t niso_animation_promise_state(niso_dom* dom, niso_handle self, bool finished, uint32_t* out);

The current ready (or finished) promise’s generation times four, plus 0 while it is pending, 1 once fulfilled and 2 once rejected.

setPromiseHook()

static operation not in JS

[NisoInternal] static undefined setPromiseHook(AnimationPromiseCallback hook);

int32_t niso_animation_set_promise_hook(niso_dom* dom, niso_animation_promise_callback_fn hook_fn, void* hook_userdata, niso_drop_fn hook_drop);

Not in niso yet

Members the web has, by the BCD keys web-features 3.45.0 lists, that idl/ doesn’t declare. The list is partial: web-features lists only the keys it maps to a feature.

• remove_filling_animation (Web animations)