When Does Requestanimationframe Fire?

It seems that requestAnimationFrame only works after first run of js code is done: https://jsfiddle.net/pn91zmpc/ var n = 0; function sleep(ms) { var date = new Da

Solution 1:

What do I need to change to see a countdown?

A lot. Never ever try to sleep in a synchronous way. This will block everything which is just bad. Instead, just use async / await, which "sleeps" in a non-blocking way:

constsleep = ms => newPromise(res =>setTimeout(res, ms));

 (asyncfunction() {
   for(let n = 0; n < 4; n++) {
     document.body.textContent = n;
     awaitsleep(1000);
   }
})();

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When does requestAnimationFrame fire?

Somewhere in the event loop. But as you block the browser synchronously, it never enters the event loop, hence it doesnt change the output.

PS: requestAnimationFrame, requests one animation frame. To update the UI multiple times, you need to call it multiple times.