Get random items of an array

Return count distinct items in random order.

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

function randomItems(values, count) {
  const pool = [...values];
  for (let i = pool.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [pool[i], pool[j]] = [pool[j], pool[i]];
  }
  return pool.slice(0, count);
}

Usage

const picks = randomItems([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 8);
picks.length; // → 8
new Set(picks).size; // → 8
randomItems(['a', 'b'], 5).length; // → 2

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 spliced the array that reduce was walking, so reduce skipped the removed positions: asking for 8 of 10 items returned 5.
• Items are distinct by position. Asking for more items than exist returns all of them, shuffled.

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.