JSFiddle - React, Tailwind, and code Playground

JavaScript

var wins = 0,
    losses = 0,
    switchDoors = confirm('In this test, should the user switch doors?'),
    doors, x, y, choice, removed;

for(x=0;x<1000;x++) {
    // Put the car behind the winning door
    doors = [0, 0, 0];
    doors[Math.floor(Math.random() * 3)] = 1;
    
    // Contestant, choose a door!
    choice = Math.floor(Math.random() * 3);
    
    // Host removes a door from the game
    removed = doors.slice(0);
    removed.splice(choice, 1);
    if (removed[0] === 0 && removed[1] === 1) {
        if (choice !== 0) removed = 0;
        else removed = 1;
    } else if (removed[0] === 1 && removed[1] === 0) {
        if (choice !== 2) removed = 2;
        else removed = 1;
    } else {
        removed = Math.floor(Math.random() * 2);
        if (choice === 0 || (choice === 1 && removed === 1)) removed++;
    }
    doors.splice(removed, 1);
    if (choice === 2 || removed === 0) choice--;
    
    // Contestant sticks with their door, or changes their choice
    if (switchDoors) choice = choice^1;
    
    if (doors[choice] === 1) wins++;
    else losses++;
}

alert('Wins: '+wins+', Losses: '+losses+', Win Rate: '+(wins/10)+'%');