createId()

Create a generator with fixed options — set the size, separator, or alphabet once and reuse it.

Signature

function createId(options?: {
  size?: number;      // default: 24
  separator?: string; // default: "_"
  alphabet?: string;  // default: base62 (0-9A-Za-z)
}): <P extends string>(prefix: P) => `${P}_${string}`

Options

Option	Type	Default	Description
size	number	24	Number of random characters (1–4096).
separator	string	"_"	Text between the prefix and the random part.
alphabet	string	base62	Characters used for the random part.

Custom size

import { createId } from "prefid";

const id = createId({ size: 16 });

id("user");  // => "user_a1b2c3d4e5f6g7h8"
id("order"); // => "order_9f8e7d6c5b4a3F2e"

const { createId } = require("prefid");

const id = createId({ size: 16 });

id("user");  // => "user_a1b2c3d4e5f6g7h8"
id("order"); // => "order_9f8e7d6c5b4a3F2e"

Custom separator

const id = createId({ separator: "-" });

id("user"); // => "user-a1b2c3d4e5f6g7h8i9j0k1l2"

Custom alphabet

Provide your own alphabet — for example, a lowercase set that omits look-alike characters for human-friendly codes.

// Lowercase, unambiguous alphabet (no 0/O/1/l)
const id = createId({ alphabet: "23456789abcdefghjkmnpqrstuvwxyz" });

id("code"); // => "code_mn7pqr2stuv9wxyz34abcdef"

For a ready-made unambiguous, case-insensitive alphabet, import the BASE32_CROCKFORD preset — the same alphabet ULID uses. It drops the ambiguous letters I, L, O, and U, so ids are safe to read aloud, print, or store in case-folding systems.

import { createId, BASE32_CROCKFORD } from "prefid";

// Crockford Base32 (the ULID alphabet): omits I, L, O, U.
const id = createId({ alphabet: BASE32_CROCKFORD });

id("code"); // => "code_MN7PQR2STVWXYZ34ABCDEFGH" — no 0/O or 1/l confusion"

const { createId, BASE32_CROCKFORD } = require("prefid");

// Crockford Base32 (the ULID alphabet): omits I, L, O, U.
const id = createId({ alphabet: BASE32_CROCKFORD });

id("code"); // => "code_MN7PQR2STVWXYZ34ABCDEFGH" — no 0/O or 1/l confusion"

Notes

size must be an integer between 1 and 4096, and alphabet must contain at least 2 characters — otherwise createId throws a RangeError. The upper bound guards against a huge size exhausting memory when the value comes from untrusted input.
A larger size or alphabet means more entropy and even lower collision odds.