# Generate an unique and increment id

Create a counter that returns 0, 1, 2… on successive calls.

Canonical: https://1loc.dev/misc/generate-an-unique-and-increment-id/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Usage lines executed in Node.js 22 and headless Chromium; no external services
Updated: 2026-10-28

## Implementation

```javascript
function createIdGenerator(start = 0) {
  let id = start;
  return () => id++;
}
```

## Usage

```javascript
const nextId = createIdGenerator();
[nextId(), nextId(), nextId()]; // → [0, 1, 2]
const other = createIdGenerator(100);
other(); // → 100
```

Lines marked → were executed in Node.js 22 and in headless Chromium, and each result was compared with the value shown. Lines marked e.g. are illustrative.

## Limits

- The original assigned to an undeclared id: a ReferenceError in strict mode and ES modules, a leaked global otherwise.
- Unique only within one process until it restarts. For IDs shared across servers, requests or retries, use crypto.randomUUID() or a database sequence.

The function does not validate its arguments. Add checks where it receives untrusted input.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/generate-an-unique-and-increment-id.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Declares the counter; the original assigned to an undeclared variable, which throws in strict mode and ES modules. Documented as a reference with executed usage lines. Original MDX retained as inert source evidence.