uuidv7-js

UUIDv7 generator library for JavaScript, RFC 9562 compliant. Supports encoding/decoding UUIDs to custom alphabets.

Installation

npm i uuidv7-js

Usage

import { UUIDv7, uuidv7, encodeUUIDv7, decodeUUIDv7 } from "uuidv7-js";

// Initialize a new UUIDv7 generator.
// You can pass a custom encoding alphabet here.
const uuid = new UUIDv7();

const id = uuid.gen(); // 018ef3e8-90e2-7be4-b4ea-4be3bf8803b7
const encoded = uuid.encode(id); // CANANjseoigQthQMd1VwC
const decoded = uuid.decode(encoded); // 018ef3e8-90e2-7be4-b4ea-4be3bf8803b7
const isValid = UUIDv7.isValid(id); // true
const timestamp = UUIDv7.timestamp(id); // 1713489088738
const date = UUIDv7.date(id); // 2024-04-19T01:11:28.738Z

// You can also use convenient function aliases if you don't need to use a custom alphabet.
const id = uuidv7(); // 018ef3e8-90e2-7be4-b4ea-4be3bf8803b7
const encoded = encodeUUIDv7(id); // CANANjseoigQthQMd1VwC
const decoded = decodeUUIDv7(encoded); // // 018ef3e8-90e2-7be4-b4ea-4be3bf8803b7

Create a new instance

const uuid = new UUIDv7(opts?: {
  encodeAlphabet?: string;
  blockOnBackwardsClock?: boolean;
})

Creates a new UUIDv7 instance.

• encodeAlphabet: alphabet used for encode / decode. Defaults to the Base58 alphabet. ASCII, 16-64 characters, no duplicates.
• blockOnBackwardsClock: when true, gen() synchronously busy-waits if the system clock goes backwards relative to the last observed timestamp, until the clock catches up. The embedded UUID timestamp will always reflect the actual wall clock at the cost of blocking the event loop for the duration of any backwards skew. Defaults to false (timestamp is pinned and the monotonic counter advances). Has no effect on the custom-timestamp path. See Implementation details.

Instance methods

gen

gen(customTimestamp?: number) => string

Generates a new UUIDv7. You can provide a custom timestamp to be used instead of the current one.

genMany

genMany(amount: number, customTimestamp?: number) => string[]

Generates a custom amount of UUIDv7s. You can provide a custom timestamp to be used instead of the current one.

encode

encode(id: string) => string

Encodes a UUIDv7 using the alphabet passed to the constructor or the default one.

decode

decode(encodedId: string) => string | null

Decodes an encoded UUIDv7 using the alphabet passed to the constuctor or the default one. If the UUIDv7 is not valid, null is returned.

decodeOrThrow

decodeOrThrow(encodedId: string) => string

Decodes an encoded UUIDv7 using the alphabet passed to the constuctor or the default one. If the UUIDv7 is not valid, an error is thrown.

Static methods

UUIDv7.isValid

UUIDv7.isValid(id: string) => boolean

Checks if the UUIDv7 is valid.

UUIDv7.timestamp

UUIDv7.timestamp(id: string) => number | null

Returns the timestamp part of the UUIDv7. If the UUIDv7 is not valid, null is returned.

UUIDv7.date

UUIDv7.date(id: string) => Date | null

Returns the timestamp part of the UUIDv7 converted to Date. If the UUIDv7 is not valid, null is returned.

Function aliases

The library provides a few function aliases for convenience. You can use them without creating a new UUIDv7 instance:

Function name	Instance method	Description
uuidv7	gen	Generates a new UUIDv7.
encodeUUIDv7	encode	Encodes a UUIDv7 with the default Base58 alphabet.
decodeUUIDv7	decode	Decodes an encoded UUIDv7 from Base58 alphabet. Returns null if the encoded ID is invalid.
decodeOrThrowUUIDv7	decodeOrThrow	Decodes an encoded UUIDv7 from Base58 alphabet. Throws an error if the encoded ID is invalid.

Implementation details

This library implements the RFC 9562 spec to generate UUIDv7s, following method 2 ("Monotonic Random") of the "Monotonicity and Counters" section. Monotonicity and uniqueness are guaranteed per UUIDv7 instance.

For the default (runtime-clock) generation path:

• if the current timestamp is ahead of the last stored one, new rand_a and rand_b parts are generated;
• if the current timestamp is behind the last stored one (clock skew, NTP step-back, VM time-warp), the timestamp is pinned to the last stored value and the monotonic counter advances. The library never busy-waits on a backwards clock by default. Opt into the v1 behavior with new UUIDv7({ blockOnBackwardsClock: true }): gen() will then synchronously wait until the wall clock catches up, at the cost of blocking the event loop for the duration of the skew;
• if the current timestamp is equal to the last stored one, rand_b is incremented by a random integer in [1, 2^32] as the primary counter. When rand_b overflows its 62 bits, rand_a is incremented by 1 as a secondary counter and rand_b is freshly seeded. When both counters overflow within one millisecond (extraordinarily rare), the timestamp is advanced by 1ms and the random parts are regenerated. RFC 9562 §6.2 permits this sub-millisecond drift.

For the custom-timestamp generation path:

• if the custom timestamp differs from the last custom timestamp, new random parts are generated;
• if it matches, the same counter logic above applies. On the extremely rare event that both counters overflow under a fixed custom timestamp, the random parts are regenerated. This breaks monotonicity for that specific case but guarantees a valid UUIDv7 is always returned without altering the caller's timestamp.

The custom-timestamp state is tracked separately from the runtime-clock state, so the two paths do not interfere.

Field and Bit Layout

This is the UUIDv7 Field and Bit Layout, took from the spec linked above:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           unix_ts_ms                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          unix_ts_ms           |  ver  |       rand_a          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|var|                        rand_b                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            rand_b                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Description

unix_ts_ms

48 bit big-endian unsigned number of Unix epoch timestamp in milliseconds as per Section 6.1. Occupies bits 0 through 47 (octets 0-5).

ver

The 4 bit version field as defined by Section 4.2, set to 0b0111 (7). Occupies bits 48 through 51 of octet 6.

rand_a

12 bits pseudo-random data to provide uniqueness as per Section 6.9 and/or optional constructs to guarantee additional monotonicity as per Section 6.2. Occupies bits 52 through 63 (octets 6-7).

var

The 2 bit variant field as defined by Section 4.1, set to 0b10. Occupies bits 64 and 65 of octet 8.

rand_b

The final 62 bits of pseudo-random data to provide uniqueness as per Section 6.9 and/or an optional counter to guarantee additional monotonicity as per Section 6.2. Occupies bits 66 through 127 (octets 8-15).

Feedback

If you found a bug in the implementation, please open a new issue.

Alternatives

• uuidv7 by LiosK

License

This project is licensed under the MIT License.