How do I create a GUID / UUID? Ask Question

[Edited 2023-03-05 to reflect latest best-practices for producing RFC4122-compliant UUIDs]

crypto.randomUUID() is now standard on all modern browsers and JS runtimes. However, because new browser APIs are restricted to secure contexts, this method is only available to pages served locally (localhost or 127.0.0.1) or over HTTPS.

For readers interested in other UUID versions, generating UUIDs on legacy platforms or in non-secure contexts, there is the uuid module. It is well-tested and supported.

Failing the above, there is this method (based on the original answer to this question):

function uuidv4() {
  return "10000000-1000-4000-8000-100000000000".replace(/[018]/g, c =>
    (+c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> +c / 4).toString(16)
  );
}

console.log(uuidv4());

Note: The use of any UUID generator that relies on Math.random() is strongly discouraged (including snippets featured in previous versions of this answer) for reasons best explained here. TL;DR: solutions based on Math.random() do not provide good uniqueness guarantees.