The Animation.startTime
property of the Animation
interface is a double-precision floating-point value which indicates the scheduled time when an animation's playback should begin.
An animation's start time is the time value of its timeline
when its target KeyframeEffect
is scheduled to begin playback. An animation's start time is initially unresolved (meaning that it's null
because it has no value).
A floating-point number representing the current time in milliseconds, or null
if no time is set. You can read this value to determine what the start time is currently set at, and you can change this value to make the animation start at a different time.
In the Running on Web Animations API example, the we can sync all new animated cats by giving them all the same startTime
as the original running cat:
const catRunning = document
.getElementById("withWAAPI")
.animate(keyframes, timing);
function addCat() {
const newCat = document.createElement("div");
newCat.classList.add("cat");
return newCat;
}
function animateNewCatWithWAAPI() {
const newCat = addCat();
const newAnimationPlayer = newCat.animate(keyframes, timing);
newAnimationPlayer.startTime = catRunning.startTime;
WAAPICats.appendChild(newCat);
}
To offer protection against timing attacks and fingerprinting, the precision of animation.startTime
might get rounded depending on browser settings. In Firefox, the privacy.reduceTimerPrecision
preference is enabled by default and defaults to 20 µs in Firefox 59; in 60 it will be 2 ms.
animation.startTime;
animation.startTime;
In Firefox, you can also enabled privacy.resistFingerprinting
, the precision will be 100ms or the value of privacy.resistFingerprinting.reduceTimerPrecision.microseconds
, whichever is larger.