Version 4 is pure randomness
A v4 UUID is 122 random bits with six bits reserved to mark the version and variant. Nothing about it encodes the time or the machine, which is exactly why two systems can mint them independently without ever agreeing on anything.
Why collisions are not a worry
With 122 random bits, you would need to generate about a billion UUIDs per second for a century before a duplicate became likely. The randomness here comes from the browser’s cryptographic generator, not Math.random.
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Frequently asked questions
Q. Are these safe to use as database keys?
Yes, though random keys scatter writes across an index. If insert throughput matters, look at UUIDv7 or a sortable scheme instead.
Q. Does case matter?
No. UUIDs are case-insensitive; lowercase is the conventional form and what most libraries emit.
Q. Where does the randomness come from?
crypto.getRandomValues in your browser — the same source used for cryptographic keys, not the weaker Math.random.