randomUIntBelow(max) returns a uniform random non-negative integer less than max (0 <= output < max). max must be at most 2^53.

import {randomUIntBelow} from "random-uint-below"


console.log(randomUIntBelow(6)); // Generates a uniform random value from [0, 1, 2, 3, 4, 5]

Since one of the most common use cases for this is to select a random element from an array, we also provide a convenience:

import {randomChoice} from "random-uint-below"

console.log(randomChoice(["vanilla", "strawberry", "peppermint"]))

random-uint-below.js requires crypto.getRandomValues, which is available in:

• All major browsers since 2014: https://caniuse.com/getrandomvalues
• bun and deno
• node without a flag since v19: https://nodejs.org/api/webcrypto.html#cryptogetrandomvaluestypedarray

Builds are only published in ESM (with ES2020 compatibility).

We no longer publish a build that modifies the global variable. You can create such a build yourself using:

# bash
cd "$(mktemp -d)" && npm init -y && npm install esbuild random-uint-below
echo 'import { randomUIntBelow } from "random-uint-below"; globalThis.randomUIntBelow = randomUIntBelow' | \
  npx esbuild --target=es6 --bundle --minify --outfile=randomUintBelow.global.js

This work is dedicated to the public domain using the Unlicense.