Generate a Version 4 UUID

This typescript function generates a UUID using the RFC 4122 specification¹.

Version 4 UUIDs take the form xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx where x is any hex digit and y is in [8, 9, a, b].

Assuming these are generated with sufficient entropy, 1B UUIDs every second for 100 years would be ~50% chance of collision²

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function generateUUIDv4(): string {
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  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, c => {
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    const r = Math.random() * 16 | 0;
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    const v = c === 'x' ? r : (r & 0x3 | 0x8);
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    return v.toString(16);
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  });
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}