MontyJS

function monty(){
  var doors = [0, 0, 0];
  var switchWins = 0;
  var keepWins = 0;

  //switching 10,000 times
  for(var i = 0 ; i < 10000 ; ++i){
    doors[Math.floor(Math.random() * 3)] = 1;
    pick = Math.floor(Math.random() * 3;
    if(doors[pick] !== 1) switchWins++;
  }
  //not switching 10,000 times
  for(var i = 0 ; i < 10000 ; ++i){
    doors[Math.floor(Math.random() * 3)] = 1;
    pick = Math.floor(Math.random() * 3;
    if(doors[pick] === 1) keepWins++;
  }
  console.log("Switch wins: " + switchWins);
  console.log("Keep wins: " + keepWins);
}