Fisher Yates Shuffle

shuffle.node.js

// Crypto PseudoRandom Shuffle: one right way to randomize, esp for gaming
// https://replit.com/@jeremybradbury/CSPRNG-Fisher-Yeats-Shuffle
// NodeJS - CJS version (backward comaptible)
const crypto = require("crypto");

// the secret sauce
const getRndInt = (bytes) =>
  parseFloat(
    parseFloat(crypto.randomBytes(bytes).toString("hex"), 16).toString(10),
    10
  );

// the SDK
function getCSPRNG(min, max) {
  // validate
  if (min == null || max == null) {
    throw new Error("min and max must be defined");
  }
  if (min < 0) {
    return console.error("min must be at least 0");
  }
  if (min > max) {
    return console.error("min must be less than max");
  }
  let bytes;
  // choose the correct array type
  switch (true) {
    case max < 1:
      console.error("max must be at least 1");
      return;
    case max < 256: // 1-255
      bytes = 1;
      break;
    case max < 65536: // 256-65535
      bytes = 2; // default
      break;
    case max < 4294967296: // 65536-4294967295
      bytes = 4;
      break;
    default:
      console.error("max must be no more than 4294967295");
      return;
  }

  let randomNumber = getRndInt(bytes);
  let attempts = 1;
  while (randomNumber > max || randomNumber < min) {
    randomNumber = getRndInt(bytes); // retry until result is in range
    attempts++; // track failed generations
  }
  // console.debug({randomNumber, attempts });
  return randomNumber;
};

// const random = () => Math.random(); // between 0 and 1
const cryptoRandom = () => getCSPRNG(0, 10) / 10; // between 0 and 1

// Fisher–Yates shuffle - https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle
function shuffle (array = []) {
  let index = array.length;
  while (index) {
    const next = Math.floor(cryptoRandom() * index--);
    const temp = array[index];
    if (array[next] == null) { // == null, includes undefined too, but not '' or 0
      continue;
    }
    array[index] = array[next]; // set to a random value
    // console.log(next, array[next]);
    array[next] = temp; // swap with the previous number
  }
  return array;
};

// implementation variables 
const getDie = (length = 6) => Array.from({ length }, (v, i) => i + 1);
const getCoin = () => getDie(2);
const langs = ['C++', 'C#', 'Java', 'JavaScript', 'Python', 'Ruby', 'PHP', 'Go', 'CSS', 'HTML', 'SQL', 'TypeScript', 'Swift', 'Kotlin', 'Rust', 'Scala'];

// usage examples - logged simplest to most complex
console.log("coin flip:", shuffle(getCoin())[0] === 1 ? 'heads' : 'tails'); // grab the first item in the array
console.log("d6 roll:", shuffle(getDie(6))[0]); // grab the first item in the array
console.log("d20 roll:", shuffle(getDie(20))[0]); // grab the first item in the array
console.log("languages winner:", shuffle(langs)[0]); // grap the first item in the array
console.log("languages shuffled:", shuffle(langs)); // show the whole array, randomized