How to generate a UUID

Short answer

crypto.randomUUID() returns a random UUID of version 4: 36 characters with hyphens:

const id = crypto.randomUUID();
 
console.log(id.length, id.split('-').length);

Output:

36 5

Checking the format

A UUID consists of hex digits in groups of 8, 4, 4, 4 and 12:

const isUuid = (value) => /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i.test(value);
 
console.log(isUuid(crypto.randomUUID()));
console.log(isUuid('123-abc'));

Output:

true
false

In Node.js

In Node.js the same function can also be imported from node:crypto:

import { randomUUID } from 'node:crypto';
 
console.log(randomUUID().length);

Output:

36

Common mistake

In the browser crypto.randomUUID() works only on secure pages: https or localhost. On a plain http page it is missing. Do not build ids from Math.random(), its values are predictable and can repeat.

console.log(typeof crypto.randomUUID);

Output:

function