proving to the kids you should always switch doors....

montyHallSim.js

const rand = (min, max) => Math.floor(Math.random() * (max - min + 1) + min);
const setRemove = (list, r1, r2) => {
    let temp = new Set(list);
    temp.delete(r1);
    temp.delete(r2);
    return [...temp];
};

const GOAT = '🐐';
const PRIZE = '🚗';

const playGame = (shouldSwitch) => {
    let doors = new Array(3).fill(GOAT);

    let prize = rand(0, 2);
    doors[prize] = PRIZE;

    let contestantsChoice = rand(0, 2);

    let removeChoices = setRemove([0, 1, 2], contestantsChoice, prize);
    let removed = removeChoices[rand(0, removeChoices.length - 1)];

    shouldSwitch = shouldSwitch === undefined ? (rand(0, 1) > 0.5 ? true : false) : shouldSwitch;

    if (shouldSwitch) {
        contestantsChoice = setRemove([0, 1, 2], contestantsChoice, removed)[0];
    }

    return contestantsChoice === prize;
};

const run = (switchStrategy) => {
    let wins = 0;
    const games = 100000;
    for (let i = 0; i < games; i++) {
        wins = playGame(switchStrategy) ? wins + 1 : wins;
    }
    return { games, wins, pct: Math.round((wins / games) * 100) };
};

let res = run(true);
console.log(`ALWAYS: Games: ${res.games}, Wins: ${res.wins}, Win %: ${res.pct}%`);

res = run(false);
console.log(`NEVER : Games: ${res.games}, Wins: ${res.wins}, Win %: ${res.pct}%`);

res = run();
console.log(`RANDOM: Games: ${res.games}, Wins: ${res.wins}, Win %: ${res.pct}%`);