JavaScript has no sleep function, but we can easily solve it this way!

In order to make your browser sleep, just write this line of code:

await new Promise(_ => setTimeout(_, 2000)); 

This will make the browser sleep for 2 seconds (2000ms).

Please note that it works in modern browsers only (> 2017)! See browser compatibility for await on caniuse.com.

Let's create a reusable sleep function

const sleep = (ms = 2000) => new Promise(_ => setTimeout(_, ms)); 

Or with a more old days' notation:

function sleep(ms = 2000) { return new Promise(function(_) { return setTimeout(_, ms) }); } 

If you want to explore other features of Promise you can browse the MDN Doc.

How to use it

console.log(`Let's wait for 5s`); await sleep(5000); // 5000ms = 5seconds console.log(`5s have passed`); 

Result in console:

> Let's wait for 5s [waiting for 5 seconds] > 5s have passed 

Top-level await issue

Using top-level await might not work in some old browser/node versions. To solve this problem we can wrap our code
with an immediately-invoked async function.

(async function() { console.log(`Let's wait for 5s`); await sleep(5000); console.log(`5s have passed`); }()); 

Sleep function in old browsers

Just a note about Sleep function in old browser: it has usually been written this way, but it's definitely not
"performance friendly".

function sleep(mss) { const date = Date.now(); let currentDate = null; do { currentDate = Date.now(); } while( currentDate - date < milliseconds); } 

Demo

I created a stackblitz project with a simple example.