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 browsers.
Explanation
There is no available sleep
function in JavaScript, but it is possible to emulate sleeping with acync
functions. The main idea is to postpone resolve
function call with setTimeout
wrapped in Promise
object. Later that create 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. Advantage because our logic will not freeze the web browser as infinity loop does.
More complicated runnable example code 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();