JavaScript - sleep function

In this short article, we're going to have a look at how in JavaScript create sleep(ms) function.

Quick solution:

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

// await sleep(1000);  // <------ use it inside async function

Node: async/await operators were introduced in ES8 (ES2017)  - use Babel or TypeScript to provide this functionality in older web browsers.

Explanation

sleep() function is not available in JavaScript, but it is possible to emulate sleeping with acync functions. The main idea is to postpone resolve() function call with setTimeout() function wrapped in Promise object. Later that created logic can be placed inside own sleep() function and called with await keyword inside async method only - it is the main disadvantage/advantage of the approach. The async sleep() function doesn't freeze the web browser as the infinity loop does that is the advantage.

A more complicated runnable example code is below:

// ONLINE-RUNNER:browser;

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


// Usage example:

const action = async () => {
    console.log('[START]');
    for (let i = 0; i < 5; ++i) {
        await sleep(1000); // sleeps 1s each iteration
        console.log(i);
    }
    console.log('[STOP]');
};

action();