app.js

const startGameBtn = document.getElementById('start-game-btn');
const ROCK = 'ROCK';
const PAPER = 'PAPER';
const SCISSORS = 'SCISSORS';
const DEFAULT_USER_CHOICE = ROCK;
const RESULT_DRAW = 'DRAW';
const RESULT_PLAYER_WINS = 'PLAYER_WINS';
const RESULT_COMPUTER_WINS = 'COMPUTER_WINS';

let gameIsRunning = false;

const getPlayerChoice = () =>
{
    const selection = prompt(`${ROCK}, ${PAPER} or ${SCISSORS}?`).toUpperCase();
    if(selection!==ROCK && selection!==PAPER && selection!==SCISSORS)
    {
        alert(`Invalid choice! We chose ${DEFAULT_USER_CHOICE} for you!`);
        return DEFAULT_USER_CHOICE;
    }
    return selection;
}

const getComputerChoice = () =>
{
    const randomValue = Math.random();
    if(randomValue < 0.34)
    {
        return ROCK;
    } else if(randomValue < 0.67)
    {
        return PAPER;
    } else 
    {
        return SCISSORS;
    }
}

const getWinner = (cChoice, pChoice = DEFAULT_USER_CHOICE) =>
    cChoice === pChoice ?
    RESULT_DRAW 
    :   (cChoice === ROCK && pChoice === PAPER) ||
        (cChoice === PAPER && pChoice === SCISSORS) ||
        (cChoice === SCISSORS && pChoice === ROCK)
    ?   RESULT_PLAYER_WINS 
    :   RESULT_COMPUTER_WINS;


    // if(cChoice === pChoice)
    // {
    //     return RESULT_DRAW;
    // } else if(
    //     cChoice === ROCK && pChoice === PAPER ||
    //     cChoice === PAPER && pChoice === SCISSORS ||
    //     cChoice === SCISSORS && pChoice === ROCK
    //     )
    // {
    //     return RESULT_PLAYER_WINS;
    // } else
    // {
    //     return RESULT_COMPUTER_WINS;
    // }


startGameBtn.addEventListener('click', () =>
{
    if(gameIsRunning)
    {
        return;
    }
    gameIsRunning = true;
    console.log('Game is starting...');
    const playerChoice = getPlayerChoice();
    const computerChoice = getComputerChoice();
    let winner; 
    if(playerChoice)
    {
        winner = getWinner(computerChoice, playerChoice);
    } else
    {
        winner = getWinner(computerChoice, playerChoice);
    }
    let message = `You chose ${playerChoice}, computer chose ${computerChoice}. Therefore, you `;
    if(winner === RESULT_DRAW)
    {
        message = message + 'had a draw.';
    } else if(winner === RESULT_PLAYER_WINS)
    {
        message = message + 'won.';
    } else 
    {
        message = message + 'lost.';
    }
    alert(message);
    gameIsRunning = false;
});