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What is the JavaScript version of sleep()?
JavaScript doesn't have a built-in sleep() function like other languages, but you can create one using Promise and setTimeout() with async/await.
Creating a Sleep Function
The most common approach is to create a promise-based sleep function that works with async/await:
<!DOCTYPE html>
<html>
<body>
<script>
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function displayMessages() {
document.write('Wait for 3 seconds!<br>');
await sleep(3000);
document.write('After 3 seconds!<br>');
document.write('Wait for 2 more seconds!<br>');
await sleep(2000);
document.write('Done!');
}
displayMessages();
</script>
</body>
</html>
How It Works
The sleep() function returns a Promise that resolves after the specified number of milliseconds. When used with await, it pauses execution of the async function without blocking the main thread.
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function example() {
console.log('Starting...');
await sleep(2000); // Wait 2 seconds
console.log('2 seconds later');
await sleep(1000); // Wait 1 second
console.log('Done!');
}
example();
Starting... 2 seconds later Done!
Alternative: Using setTimeout Directly
Without async/await, you can use setTimeout() with callbacks:
<!DOCTYPE html>
<html>
<body>
<script>
console.log('Starting...');
setTimeout(() => {
console.log('After 2 seconds');
setTimeout(() => {
console.log('After 4 seconds total');
}, 2000);
}, 2000);
</script>
</body>
</html>
Comparison
| Method | Readability | Modern JS |
|---|---|---|
| Promise + async/await | High | Yes |
| setTimeout callbacks | Low (callback hell) | No |
Conclusion
Use Promise with async/await to create a clean sleep function in JavaScript. This approach is non-blocking and follows modern JavaScript best practices.
Updated on: 2026-03-15T21:42:21+05:30
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