Generate a UUID in JavaScript

A Universally Unique Identifier (UUID) is a 128-bit number used to uniquely identify some object or entity on the Internet. It has been standardized by RFC 4122.

As browsers and Node.js have historically had some differences in their APIs, you should be aware of the runtime environment when generating a UUID. Let's dive into your options and when to use them.

Latest browsers & Node.js versions

Generating a UUID in a modern browser or Node.js is very straightforward. As the Crypto API has been standardized you can use the crypto.randomUUID() method to generate a UUID.

crypto.randomUUID(); // '7982fcfe-5721-4632-bede-6000885be57d'

import { randomUUID } from 'crypto';

randomUUID(); // '7982fcfe-5721-4632-bede-6000885be57d'

Older environments

In older environments, generating a UUID is a more complex task. While the technique described below is going to be less relevant as time goes by, I think it's still worth documenting.

If crypto.randomUUID() is not an option, crypto.getRandomValues() should still be available. This method allows you to generate cryptographically strong pseudo-random data. It accepts a TypedArray as an argument and fills it with random values.

Start by creating a string that represents a UUID template: ([1e7] + -1e3 + -4e3 + -8e3 + -1e11). This string contains placeholders (the numbers 0, 1, and 8) that will be replaced with random hexadecimal digits.

Then, using String.prototype.replace(), replace the placeholders with the random hexadecimal digits that we generate using crypto.getRandomValues(). For each matching placeholder, use the bitwise XOR operator (^) and the right shift (>>) by the result of c / 4 (where c is the placeholder). This will result in a random hexadecimal digit. Finally, use Number.prototype.toString() with a radix of 16 to convert the value to a hexadecimal string.

const generateUUID = () =>
  ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
    (
      c ^
      (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))
    ).toString(16)
  );

generateUUID(); // '7982fcfe-5721-4632-bede-6000885be57d'