Tiny seedable PRNG in JavaScript

gistfile1.txt

/**
 * A lightweight seedable RNG for generating low-quality random numbers.
 *
 * I find this mostly useful in testing and Storybook, where I want to
 * repeatably generate a sequence of random numbers, but I don't need
 * cryptographically strong randomness. It's only useful in those
 * circumstances. Otherwise...
 *
 * - If it doesn't need to be repeatable, just use JS's native "Math.random()"
 * - If it needs to be cryptographically strong, import a reliable PRNG package
 *
 * This function uses the Lehmer RNG algorithm, which is considered pretty
 * weak by modern PRNG standards but is fine for low-stakes purposes.
 * @see https://en.wikipedia.org/wiki/Lehmer_random_number_generator
 * @see https://github.com/tc39/proposal-seeded-random
 * @example
 *
 * // Seed it.
 * const rand = seedPseudoRand(10);
 *
 * // Generate a random integer between 0 and 99 (inclusive)
 * const n = rand() % 100;
 *
 * // Generate a random float between 0 and 1 (inclusive)
 * const f = rand() / PSEUDO_RAND_MAX;
 *
 * @param {number} [seed=1] A seed for the RNG. Must be a positive integer
 * greater than 0. (Each RNG seeded with the same integer, will return the same sequence of
 * random integers.)
 * @returns {function():number} A function that will return a "random" integer
 * between 0 and PSEUDO_RAND_MAX (0x7ffffffe), inclusive, each time that it is called.
 */
export function seedPseudoRand(seed = 1) {
  const rand = function pseudoRand() {
    seed = (seed * 48271) % MODULUS;
    return seed;
  };
  // With the default seed of 1, the first result is 48271, and it'll be similarly small if
  // the seed is any small integer. So clear out that first result for nicer-looking results.
  rand();
  return rand;
}
const MODULUS = 0x7fffffff
/**
 * The largest number the PRNG can return.
 */
export const PSEUDO_RAND_MAX = MODULUS - 1;