Using JavaScript async instead of setInterval

Question

Let's say I want to run the function update() every second.

I can do that in two ways:

async function interval() {
  await new Promise((res, req) => { 
    setTimeout(res, 1000)
  })
  update()
  interval()
}

or

setInterval(update, 1000)

Is there any functional difference between the two?

You can catch interval if you use a promise: `interval().catch(err=>...)` — HMR, Dec 29 '17 at 08:34
You can cancel `setInterval` but cant cancel the `Promise` implementation — Ayush Gupta, Dec 29 '17 at 08:38

score 0 · Answer 1 · edited Dec 29 '17 at 09:13

0

The difference is that your interval functions returns a promise for when it is finished. You will need to add a return though so that it works properly:

async function interval() {
  await new Promise((res, req) => { 
    setTimeout(res, 1000)
  })
  update()
  return interval()
//^^^^^^
}

Now when update throws an exception, the promise is rejected and you can .catch() the error. Also the interval recursive calls would stop running, in contrast to the setInterval which would just continue.

Also async/await syntax has the advantage that you can avoid recursion to create loops:

async function interval() {
  while (true) {
    await new Promise((res, req) => { 
      setTimeout(res, 1000)
    })
    update()
  }
}

edited Dec 29 '17 at 09:13

Akshay Vijay Jain

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answered Dec 29 '17 at 08:39

Bergi

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when update throws an exception, promise will not be rejected!, promise has no connection with update function – Akshay Vijay Jain Dec 29 '17 at 08:59
@AkshayVijayJain Of course it does! The promise returned by `interval()` is rejected when any of the code inside the body throws an exception. Including the `update()` call. – Bergi Dec 29 '17 at 09:03
why do you think interval() is returning promise? – Akshay Vijay Jain Dec 29 '17 at 09:04
@AkshayVijayJain Uh, because it's an `async function`? That's how async/await works. – Bergi Dec 29 '17 at 09:13

score 0 · Answer 2 · answered Dec 29 '17 at 08:54

Your question is asking difference between settimeout and setinterval to achieve repetition, I feel here there is no relevance of asycn/await, you have just used it to avoid calling same function in setTimeout.

Or you might say the relevance is async/await is doing, what setTimeout does, however as pointed by Ayush, you do not have any option to cancel the loop, which you get with setTimeout

So following link might answer your curiosity.
setTimeout or setInterval?

Thanks

Using JavaScript async instead of setInterval

2 Answers2

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