monty.js

var wouldWinIfSwitch = 0;
var wouldLoseIfSwitch = 0;
var gameQty = 0;
function runGame() {
    var prizeDoor = Math.floor(3 * Math.random());
    var guessDoor = Math.floor(3 * Math.random());
    var firstGuessIsRight = (guessDoor === prizeDoor);
    
    if ( firstGuessIsRight ) {
        ++wouldLoseIfSwitch;
    } else {
        ++wouldWinIfSwitch;
    }
    
    ++gameQty;
}