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    ULID generator for NodeJS and the browser

    ulidx Tests status

    ULID generator library, based off of the original ulid for NodeJS and the browser. ULIDs are Universally Unique Lexicographically Sortable Identifiers. This library adheres to this specification.

    The original ulid is no longer maintained, and has several outstanding compatibility-related issues that were never addressed. This library aims to address those and remain compatible in a larger range of environments.


    Install using npm by running: npm install ulidx --save.

    ulidx provides types and is written entirely in Typescript.


    Import ulid to generate new ULIDs:

    import { ulid } from "ulidx";
    ulid(); // 01F7DKCVCVDZN1Z5Q4FWANHHCC

    Time seed

    You can also provide a time seed which will consistently give you the same string for the time component.

    This is useful for migrating to ulid.

    ulid(1469918176385); // 01ARYZ6S41TSV4RRFFQ69G5FAV

    Monotonic ULID factory

    To generate monotonically increasing ULIDs, create a monotonic counter using the factory:

    import { monotonicFactory } from "ulidx";
    const ulid = monotonicFactory();
    // Strict ordering for the same timestamp, by incrementing the least-significant random bit by 1
    ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVR8
    ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVR9
    ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVRA
    ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVRB
    ulid(150000); // 000XAL6S41ACTAV9WEVGEMMVRC
    // Even if a lower timestamp is passed (or generated), it will preserve sort order
    ulid(100000); // 000XAL6S41ACTAV9WEVGEMMVRD

    Decode ULID Time

    Import decodeTime to extract the timestamp embedded in a ULID:

    import { decodeTime } from "ulidx";
    // Extract milliseconds since UNIX Epoch from ULID
    decodeTime("01ARYZ6S41TSV4RRFFQ69G5FAV"); // 1469918176385

    Pseudo-Random Number Generation (PRNG)

    ulidx will attempt to locate a suitable cryptographically-secure random number generator in the environment where it's loaded. On NodeJS this will be crypto.randomBytes and in the browser it will be crypto.getRandomValues.

    Math.random() is not supported: The environment must have a suitable crypto random number generator.


    ulidx is compatible with the following environments:

    • NodeJS 10 and up
      • Node REPL
    • Browsers with working crypto / msCrypto libraries
      • Web workers

    ulidx is not compatible with Cloudflare Workers due to their problematic stance on getting the current time.


    ulidx is not currently bundled for web - you can do this yourself using a tool like Webpack or Rollup. You should absolutely disable polyfills for crypto in this case, as ulidx will use the built-in crypto global API rather than any polyfilled crypto anyway. Including a polyfill for crypto will just bloat your application.


    React-Native support, with synchronous PRNG is a goal of this library. No ETA, however.


    npm i ulidx

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    • perrymitchell