GuideGeneratorDetailed Guide

How to Build a Random Number Generator

A random number generator produces unpredictable numbers for games, simulations, sampling, and security applications. Different use cases require different types of randomness.

What is a Random Number Generator?

Random number generators (RNGs) can be pseudo-random (algorithmic, reproducible with seed) or true random (based on physical phenomena). Cryptographic applications require cryptographically secure RNGs.

Code Example

JavaScript

// Basic random number in range
function randomInRange(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

// Cryptographically secure random
function secureRandom(min, max) {
  const range = max - min + 1;
  const bytesNeeded = Math.ceil(Math.log2(range) / 8);
  const randomBytes = crypto.getRandomValues(new Uint8Array(bytesNeeded));
  const randomValue = randomBytes.reduce((acc, byte) => acc * 256 + byte, 0);
  return min + (randomValue % range);
}

// Generate multiple unique random numbers
function randomUniqueSet(min, max, count) {
  const set = new Set();
  while (set.size < count && set.size < (max - min + 1)) {
    set.add(randomInRange(min, max));
  }
  return Array.from(set);
}

// Weighted random selection
function weightedRandom(items, weights) {
  const totalWeight = weights.reduce((sum, w) => sum + w, 0);
  let random = Math.random() * totalWeight;
  for (let i = 0; i < items.length; i++) {
    random -= weights[i];
    if (random <= 0) return items[i];
  }
  return items[items.length - 1];
}