I am new to javascript and I made a simple Rock Paper scissor game with User Interface. There will be 5 rounds and user will play against the computer by clicking any of the three buttons.

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Review my code:


<!DOCTYPE html>
    <meta charset="UTF-8" />
    <title>Rock Paper Scissors</title>
    <link rel="stylesheet" href="style.css" />

    <h1 class="header">Rock Paper and Scissors</h1>
    <div class="round">Round 1</div>
    <div class="options">
      <button class="rock">Rock</button>
      <button class="paper">Paper</button>
      <button class="scissor">Scissor</button>
    <div class="result"></div>
    <div class="score"></div>
    <script type="text/javascript" src="external.js"></script>

Javascript code:

let playerScore = 0,
  computerScore = 0;

//generate random choice
function getComputerChoice(choices) {
  return choices[Math.floor(Math.random() * choices.length)];

function playRound(event) {
  //declare a variable playerSelection and store the event nodes class
  let playerSelection = event.target.classList.value;

  //take the computer choice in another variable
  let computerSelection = getComputerChoice(["ROCK", "PAPER", "SCISSOR"]);

  //create two variables that'll reference to divs result and score
  const resultDiv = document.querySelector(".result");
  const scoreDiv = document.querySelector(".score");
  let result;

  //after any condition is met, increment each player's score and update the result
  if (playerSelection != null) playerSelection = playerSelection.toUpperCase();
  if (playerSelection === computerSelection) {
    result = `It's a tie!`;
  } else if (
    (playerSelection === "ROCK" && computerSelection === "SCISSOR") ||
    (playerSelection === "PAPER" && computerSelection === "ROCK") ||
    (playerSelection === "SCISSOR" && computerSelection == "PAPER")
  ) {
    result = `You won ${playerSelection} beats ${computerSelection}`;
  } else {
    result = `You lose ${computerSelection} beats ${playerSelection}`;

  //update div.result
  resultDiv.textContent = result;
  //update score
  scoreDiv.textContent = `You : ${playerScore} Computer : ${computerScore}`;

function playGame() {
  let counter = 0;
  //call the addeventlistener  'click'  and update the score div consequently
  const options = document.querySelector(".options");
  options.addEventListener("click", (event) => {
    const isButton = event.target.nodeName === "BUTTON";
    if (!isButton || counter >= 5) {
    const round = document.querySelector(".round");
    if (counter < 5) {
      round.textContent = `Round ${counter + 1}`;
    } else {

//after game ends
function displayWinner() {
  const round = document.querySelector(".round");
  if (computerScore > playerScore) round.textContent = "Computer won :/";
  else if (playerScore > computerScore) round.textContent = "You won!";
  else round.textContent = "Nobody won the game ";
//calling the function

1 Answer 1


General points

  • Try to make the code self explanatory and avoid adding comment that state the obvious.

  • Avoid repeated DOM queries, use variables to store elements once when your code first starts.

  • Isolate your code from the global scope. There are many ways to do this. A tried and true method is to wrap the code in a function that is immediately run. Called an Immediately Invoked Function Expression (IIFE). See rewrite.

  • Try to keep variable names short.

  • Its is a bad habit not to wrap all blocks in {}. Example

    Bad habit

    if (foo) bar = 2;


    if (foo) { bar = 2; }
  • Try to make functions generic and reusable. For example the function getComputerChoice which select a random item from an array could be called randomItem. You can add this to a JS file with other random functions that you can use in other project.

  • Store magic values (strings and numbers) in constants. Place these constants in one place.

  • Avoid giving functions too many tasks or not clearly defining the tasks by spreading them between functions.

The DOM and JS

  • Use element IDs to uniquely locate elements rather than the class name.

  • Use data property to store data in the markup.

    Or it is most times best to create game related elements via code rather than as a static page. This give you far greater control over the visuals and associated data. But keeping it simple the rewrite adopts your design.


/* Common reusable functions */
const rndItem = arr => arr[Math.random() * arr.length | 0];
const query = qStr => document.querySelector(qStr);

    const MAX_ROUNDS = 5;
    const HANDS = ["ROCK", "PAPER", "SCISSOR"];
    const WINS = [{hand: HANDS[0], beats: HANDS[2]}, {hand: HANDS[1], beats: HANDS[0]}, {hand: HANDS[2], beats: HANDS[1]}];
    const isWin = (winHand, beatsHand) => WINS.some(w => w.hand === winHand && w.beats === beatsHand);
    const resultEl = query("#result");
    const scoreEl = query("#score");    
    const roundEl = query("#round");
    query("#options").addEventListener("click", playRound);

    const game = {
        plyScore: 0,
        plyHand: null,
        compScore: 0,
        compHand: null,
        round: 0,
        reset() {
            game.round = game.compScore = game.plyScore = 0;
            game.compHand = game.plyHand = null;

    function startGame() {
        resultEl.textContent = "New Game. Best out of " + MAX_ROUNDS + " games";
    function displayResult() { 
        var result = "It's a tie!";
        if (isWin(game.plyHand, game.compHand)) {
            result = `You won ${game.plyHand} beats ${game.compHand}`;
            game.plyScore ++;
        } else if (isWin(game.compHand, game.plyHand)) {
            result = `You lose ${game.compHand} beats ${game.plyHand}`;
            game.compScore ++;
        resultEl.textContent = "Results for round " + game.round  + " " + result;
        scoreEl.textContent = `Scores You: ${game.plyScore} Computer: ${game.compScore}`;
    function displayEndGame() { 
        if (game.round === MAX_ROUNDS) {
            let result = "The match is a draw!";
            result = game.plyScore > game.compScore ? 
                `You win the match! ${game.plyScore} rounds to ${game.compScore}` : result;
            result = game.compScore > game.plyScore ? 
                `Computer wins the match! ${game.compScore} rounds to ${game.plyScore}` : result;
            roundEl.textContent = result;
    function playRound(event) {
        if (game.round < MAX_ROUNDS && event.target.dataset.hand) {
            game.round ++;
            game.plyHand = event.target.dataset.hand;
            game.compHand = rndItem(HANDS);
<h1 class="header">Paper Scissor Rocks</h1>
    <div id="round" class="round">Select a hand to play</div>
    <div id="options" class="options">
      <button id="rock" class="rock" data-hand="ROCK">Rock</button>
      <button id="paper" class="paper" data-hand="PAPER">Paper</button>
      <button id="scissor" class="scissor" data-hand="SCISSOR">Scissor</button>
    <div id="result" class="result"></div>
    <div id="score" class="score"></div>


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