1.js

export function animationInterval(ms, signal, callback) {
  // Prefer currentTime, as it'll better sync animtions queued in the 
  // same frame, but if it isn't supported, performance.now() is fine.
  const start = document.timeline ? document.timeline.currentTime : performance.now();

  function frame(time) {
    if (signal.aborted) return;
    callback(time);
    scheduleFrame(time);
  }

  function scheduleFrame(time) {
    const elapsed = time - start;
    const roundedElapsed = Math.round(elapsed / ms) * ms;
    const targetNext = start + roundedElapsed + ms;
    const delay = targetNext - performance.now();
    setTimeout(() => requestAnimationFrame(frame), delay);
  }

  scheduleFrame(start);
}

2.js

// Usage
import { animationInterval } from './1.js';

const controller = new AbortController();

// Create an animation callback every second:
animationInterval(1000, controller.signal, time => {
  console.log('tick!', time);
});

// And to stop it:
controller.abort();

Is this gist something i can use to create a countdown timer with? like to a specific date. Or would this not be for something like that?

@zizifn no, that still drifts. That's why the code in this gist is more complicated.

@stevengrimaldo

Is this gist something i can use to create a countdown timer with?

Yes

The video is very interesting and I benefited a lot from it. 👍

Now the time obtained each time requestAnimationFrame(frame) is executed is accurate, but due to the use of setTimeout, the main thread will still be blocked and the number of seconds will jump.

Suppose there is a time-consuming synchronization task:

function animationInterval(ms, signal, callback) {
  // Prefer currentTime, as it'll better sync animtions queued in the
  // same frame, but if it isn't supported, performance.now() is fine.
  const start = document.timeline ? document.timeline.currentTime : performance.now()

  function frame(time) {
    if (signal.aborted) return
    callback(time)
    scheduleFrame(time)
  }

  function scheduleFrame(time) {
    const elapsed = time - start
    const roundedElapsed = Math.round(elapsed / ms) * ms
    const targetNext = start + roundedElapsed + ms
    const delay = targetNext - performance.now()
    setTimeout(() => requestAnimationFrame(frame), delay)
  }

  scheduleFrame(start)
}


let count = 0
function longRunningTask() {
  console.time('long task')
  for (let i = 0; i < 1500000000; i++) {
    count += 1
  }
  console.timeEnd('long task')
}

const controller = new AbortController()

// 👇
setTimeout(() => longRunningTask(), 5000)

// Create an animation callback every second:
animationInterval(1000, controller.signal, time => {
  console.log('tick!', time)
})

// And to stop it:
// controller.abort()

The actual performance is as follows:

tick! 1161.4
tick! 2144.9
tick! 3161.7
tick! 4161.3
tick! 5161.4
long task: 8215.17578125 ms
tick! 13381.1
tick! 14148.2
tick! 15148.4
tick! 16148.6
tick! 17148.8
...

Assuming there is a time-consuming task, it seems that the only way is to put this time-consuming task into a Worker or adopt a time-slicing solution to divide it into several small tasks so that the main thread has time to update the UI, right?

@jakearchibald

If your thread is blocked, then both setTimeout and requestAnimationFrame callbacks will be delayed. Avoid running long tasks on the UI thread.

I came up with a similar algo that compensates clock skew as it goes. It will compensate end to end for slight delays in setTimeout, requestAnimationFrame, and of course callback executions. So if any of these skew the clock, it will tell the next run to execute a bit earlier. As a bonus, I also made it compatible with useEffect for react users.

type ExecutionControl = { stopped?: true; animationId?: number; timeoutId?: NodeJS.Timeout };

export function interval(cb: () => void, ms: number, exeCtl: ExecutionControl = {}) {
  if (exeCtl.stopped) return;

  const start = performance.now();
  exeCtl.animationId = requestAnimationFrame(() => {
    exeCtl.timeoutId !== undefined && cb();
    const end = performance.now();
    const diff = Math.round(end - start);
    const timeout = Math.max(0, ms - diff);

    exeCtl.timeoutId = setTimeout(() => {
      return interval(cb, ms, exeCtl);
    }, timeout);
  });

  return () => {
    exeCtl.stopped = true;
    exeCtl.timeoutId && clearTimeout(exeCtl.timeoutId);
    exeCtl.animationId && cancelAnimationFrame(exeCtl.animationId);
  };
}

Fwiw, the OP solution isn't incompatible with useEffect.

useEffect(() => {
  const controller = new AbortController();

  animationInterval(1000, controller.signal, () => {
    // Runs every second
  });

  return () => controller.abort();
}, [...whatever]);