Generate an unique and increment id

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

JavaScriptNode.js & browsers Version 1.0.0 · MIT · .md

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

Usage

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.

Know the 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 above is the code the usage lines run. It does not validate its arguments; add checks where it receives untrusted input.

Keep exploring

• Convert Celsius to Fahrenheit — Apply the temperature conversion without rounding the result.
• Convert hex to RGB — Expand #rgb if needed and read the red, green and blue channels.
• Convert URL parameters to object — Read a query string into an object; repeated keys become arrays.