game.js

const rock = "rock";
const scissors = "scissors";
const paper = "paper";

function play(game, player1, player2) {
    let score = {...game.score};
    let winner = undefined;

    if (player1 === rock) {
        playHand(player2, score, scissors, paper);
    }

    if (player1 === paper) {
        playHand(player2, score, rock, scissors);
    }

    if (player1 === scissors) {
        playHand(player2, score, paper, rock);
    }

    if (score.player1 === 2) {
        winner = 1;
    }

    if (score.player2 === 2) {
        winner = 2;
    }

    return {winner: winner, score: score};

    function playHand(opponent, score, beats, losesTo) {
        if (opponent === beats) {
            score.player1++;
        } else {
            if (opponent === losesTo) {
                score.player2++;
            }
        }
    }
}

module.exports = {play, rock, paper, scissors};