read-only
Returns a Future that completes just before the window is about to repaint so the user can draw an animation frame.
If you need to later cancel this animation, use requestAnimationFrame
instead.
The Future
completes to a timestamp that represents a floating
point value of the number of milliseconds that have elapsed since the page
started to load (which is also the timestamp at this call to
animationFrame).
Note: The code that runs when the future completes should call
animationFrame
again for the animation to continue.