Function monotonicUlid

monotonicUlid(seedTime?): string

Generate a ULID that monotonically increases even for the same millisecond, optionally passing the current time. If the current time is not passed, it will default to Date.now().

Unlike the ulid function, this function is guaranteed to return strictly increasing ULIDs, even for the same seed time, but only if the seed time only ever increases. If the seed time ever goes backwards, the ULID will still be generated, but it will not be guaranteed to be monotonic with previous ULIDs for that same seed time.

Parameters

seedTime: number = ...
The time to base the ULID on, in milliseconds since the Unix epoch. Defaults to Date.now().

Returns string

A ULID that is guaranteed to be strictly increasing for the same seed time.

Example: Generate a monotonic ULID

import { monotonicUlid } from "@std/ulid";

monotonicUlid(); // 01HYFKHG5F8RHM2PM3D7NSTDAS
monotonicUlid(); // 01HYFKHG5F8RHM2PM3D7NSTDAT
monotonicUlid(); // 01HYFKHHX8H4BRY8BYHAV1BZ2T

Example: Generate a monotonic ULID with a seed time

import { monotonicUlid } from "@std/ulid";

// Strict ordering for the same timestamp, by incrementing the least-significant random bit by 1
monotonicUlid(150000); // 0000004JFHJJ2Z7X64FN2B4F1Q
monotonicUlid(150000); // 0000004JFHJJ2Z7X64FN2B4F1R
monotonicUlid(150000); // 0000004JFHJJ2Z7X64FN2B4F1S
monotonicUlid(150000); // 0000004JFHJJ2Z7X64FN2B4F1T
monotonicUlid(150000); // 0000004JFHJJ2Z7X64FN2B4F1U

// A different timestamp will reset the random bits
monotonicUlid(150001); // 0000004JFHJJ2Z7X64FN2B4F1P

// A previous seed time will not guarantee ordering, and may result in a
// ULID lower than one with the same seed time generated previously
monotonicUlid(150000); // 0000004JFJ7XF6D76ES95SZR0X