JavaScript Sleep Function

There are many use cases for making your application wait a few seconds before doing executing another task. One example is if you are making multiple API calls, you might need to wait between requests to avoid being rate limited. In other programming languages like Python and Go, these languages have built in function for this type of functionality. For example, Python has time.sleep(4) and Go has time.sleep(3 * time.Second).

JavaScript does not have a built in function, but we can easily create a function to do this functionality for us by using setTimeout. If you are not familiar, setTimeout is a built in function that will call a function that is provided as an argument after a specified number of milliseconds.

Example:

setTimeout(() => { console.log('Hello'); }, 3000);

This will log the message hello to the console after 3000 milliseconds.

To implement this in a clean and readable way, we will use a Promise.

function sleep(milliseconds) {
  return new Promise((resolve) => setTimeout(resolve, milliseconds));
}

Now, we can use this function in other async functions like so:

async function example() {
  console.log('message before sleep');
  await sleep(1000);
  console.log('message after sleep');
}

example();

One important thing to remember is that this function does not pause your entire application like it might in other programming languages. Due to how the event loop works in JavaScript, this will only pause the execution of your function.