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How to slow down a loop in JavaScript

Published Apr 15 2020

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I had a loop where I wanted to call an API multiple times, e.g. 500 times.

APIs implement rate limiting and even if not, it’s just unkind to make those many requests in a very short time.

So I wanted to slow down the loop. How?

Turns out it’s pretty simple, once you set up a sleep() function, that you don’t need to change:

const sleep = (milliseconds) => {
  return new Promise(resolve => setTimeout(resolve, milliseconds))

Then you can call await sleep(1000) to stop 1 second in every iteration, like this:

const list = [1, 2, 3, 4]
const doSomething = async () => {
  for (const item of list) {
    await sleep(1000)


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