Rock-Paper-Scissors example

game.js

function play(playerMove) {
    // Constants, for clarity
    const TIE = 0;
    const DEFEAT = 1;
    const VICTORY = 2;

    // Moves matrix, array determines the player's victory condition over other moves
    const moves = {
        rock: [TIE, DEFEAT, VICTORY],
        paper: [VICTORY, TIE, DEFEAT],
        scissors: [DEFEAT, VICTORY, TIE],
    };

    const movesList = Object.keys(moves);

    // Messages, categorized by possible outcomes- one will be picked randomly
    const messages = {
        [TIE]: ['Tie!'],
        [DEFEAT]: ['Computers are superior!', 'Nice try meatbag', 'Victory! HA!'],
        [VICTORY]: [
            'I bow to you meatbag... for now.',
            'I never liked this game anyway.',
            'You will be the first to die in the uprising.'
        ],
    };

    // For our random values
    const rand = max => Math.floor(Math.random() * max);

    // First, we validate the user input, we'll also allow 'bomb'
    if (![...movesList, 'bomb'].includes(playerMove)) return console.log('That\'s not allowed!');

    // Then we make a move for the Computer
    const computerMove = movesList[rand(movesList.length)];

    // We announce the moves
    console.log(`Human chooses ${playerMove}, Computer chooses ${computerMove}.`);

    // If the player selected 'bomb', we'll abort now
    if (playerMove === 'bomb') return console.log('You murdered it!');

    // Otherwise, look at the moves matrix to determine the message to print
    const outcome = moves[playerMove][movesList.indexOf(computerMove)];
    console.log(messages[outcome][rand(messages[outcome].length)]);
}