Generate a random string with given length

Return a lowercase Base32 identifier from a cryptographic generator.

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

function randomId(length) {
  const alphabet = '0123456789abcdefghjkmnpqrstvwxyz';
  return Array.from(crypto.getRandomValues(new Uint8Array(length)), byte => alphabet[byte % 32]).join('');
}

Usage

const id = randomId(12);
id.length; // → 12
/^[0-9a-hjkmnp-tv-z]+$/.test(id); // → true
randomId(12); // e.g. 'k3x9m2q7v0ad'

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

• 32 symbols (Crockford’s Base32, lowercase) divide 256 evenly, so every symbol is equally likely without rejection sampling. It omits i, l, o and u, which are easy to misread.
• The original took one base-36 digit from Math.random().toString(36): predictable, and empty for some values such as 0.
• Each character carries 5 bits: 26 characters give 130 bits.

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

• Generate a random boolean — Return true or false with equal probability.
• Generate a random floating point number in given range — Scale Math.random into [min, max).
• Generate a random hex color — Return a #rrggbb color from 24 random bits.