3_doors.html

<label>
    <span>Always switch:</span>
    <input type="checkbox" name="change" id="change" />
    
</label>
<button type="button" id="btn">Loop</button>​

3_doors.js

var gameshow = (function() {
    var doors = [1, 0, 0];
    
    return function(change) {
        doors.shuffle();
        
        var picked = 0, //TODO- make random?
            prize = doors.indexOf(1),
            revealed;
        
        if(picked == prize) {
            revealed = $random(1, 2);
        } else {
            if(prize == 1) {
                revealed = 2;
            } else if (prize == 2) {
                revealed = 1;
            }
        }
        
        if(change) {
            picked = revealed > 1 ? 1 : 0;
        }
        
        return picked == prize;
        
    };
})();

var loop = function(times, change) {
    var attempts = times,
        wins = 0;
    for(var i = 0; i < attempts; i ++) {
        wins += gameshow(change) ? 1 : 0;        
    };
    return wins;
    //alert('Wins: '+wins+', Attempts: '+attempts+', Percent: '+(wins/attempts));
}

    
    var change = false,
        changeToggle = $('change');

    changeToggle.addEvent('click', function() {
        change = !change;
        var msg = new Element('p', { 'html': '------ Changed to <b>' + (change ? 'Always' : 'Never') + '</b> Switch ---------' });
        msg.inject(document.body);
    });
    $('btn').addEvent('click', function() { 
        var attempts = 1000,
            wins = loop(1000, change);
        
            var para = new Element('p', { 'text': 'Wins: '+wins+', Attempts: '+attempts+', Percent: '+(wins/attempts) });
            para.inject(document.body);
    });


changeToggle.inject(document.body);
btn.inject(document.body);

​