Window.requestAnimationFrame()

The window.requestAnimationFrame() method tells the browser that you wish to perform an animation and requests that the browser calls a specified function to update an animation before the next repaint.

The method takes a callback as an argument to be invoked before the repaint.

Note: Your callback routine must itself call requestAnimationFrame() again if you want to animate another frame at the next repaint. requestAnimationFrame() is 1 shot.

You should call this method whenever you're ready to update your animation onscreen. This will request that your animation function be called before the browser performs the next repaint. The number of callbacks is usually 60 times per second, but will generally match the display refresh rate in most web browsers as per W3C recommendation. requestAnimationFrame() calls are paused in most browsers when running in background tabs or hidden <iframe>s in order to improve performance and battery life.

The callback method is passed a single argument, a DOMHighResTimeStamp, which indicates the current time (based on the number of milliseconds since time origin). When multiple callbacks queued by requestAnimationFrame() begin to fire in a single frame, each receives the same timestamp even though time has passed during the computation of every previous callback's workload (in the code example below we only animate the frame when the timestamp changes, i.e. on the first callback). This timestamp is a decimal number, in milliseconds, but with a minimal precision of 1ms (1000 µs).

Example

In this example, an element is animated for 2 seconds (2000 milliseconds). The element moves at a speed of 0.1px/ms to the right, so its relative position (in CSS pixels) can be calculated in function of the time elapsed since the start of the animation (in milliseconds) with 0.1 * elapsed. The element's final position is 200px (0.1 * 2000) to the right of its initial position.

const element = document.getElementById('some-element-you-want-to-animate'); 
let start;

function step(timestamp) {
  if (start === undefined)
    start = timestamp;
  const elapsed = timestamp - start;

  // `Math.min()` is used here to make sure that the element stops at exactly 200px.
  element.style.transform = 'translateX(' + Math.min(0.1 * elapsed, 200) + 'px)';

  if (elapsed < 2000) { // Stop the animation after 2 seconds
    window.requestAnimationFrame(step);
  }
}

window.requestAnimationFrame(step);