A very very silly implementation of the game Rock-Paper-Scissors

function game(guess){
    return (Math.round(guess.charCodeAt()%110/1.2)+1-~~(Math.random()*3))%3-1
}

function gameDebuggable(g, debug){
    var b = ~~(Math.random()*3)
        , g = Math.round(g.charCodeAt()%110/1.2)-2
        , result = (g-b+3)%3-1

    if (debug){ debug(b,g,result) }
    return result

}

function test(debug){
    var n = debug ? 100 : 100000
        , i = n
        , won = 0
        , lost = 0
        , g
        , opts = ['paper','rock', 'scissors']

    function d(b,g,r){
        console.log('comp', opts[b])
        console.log('player', opts[g])
        console.log('result', r)
        console.log('------------------' )
    }

    while(--i>0){
        g = gameDebuggable(opts[~~(Math.random()*3)], debug&&d)
        if ( g > 0 ){
            won++
        } else if (g == 0) {
            lost++
        }
    }
    return won/n
}

console.log('should be very close to 0.33:',test(1))

Please take note, that I was just kidding around with this, so there are probably many shorter versions of the same functionality. I was not trying to find those.

The two game functions are essentially the same, only difference is that one of them accepts a function for debugging.