javascript - Trying to set a span element equal to a variable value in a JS Rock, Paper, Scissors Game

Question

I'm writing a program to play rock, paper, scissors. As I was coding, everything was going fine until I added the:

userScore_span.InnerHTML = userScore;

line. When testing out the win function, I added a console.log('you win'); and it worked fine, but as soon as I added the line from above I got an error when I pressed any one of the three buttons.

I'm trying to relay the result from userScore to userScore_span given that userScore increases after a game is won

userScore++;
userScore_span.innerHTML = userScore;

However, when I press any of the buttons I get an error of:

Uncaught TypeError: Cannot set property 'innerHTML' of null
at lose (app.js:34)
at game (app.js:58)

I am not sure what the chrome Dev tools means by this. How can this be fixed?

let userScore = 0;
let computerScore = 0;
const userScore_span = document.getElementById("user-score");
const computerScore_span = document.getElementById("computer-score");
const scoreBoard_div = document.querySelector(".score-board");
const result_p = document.querySelector(".result > p");
const rock_div = document.getElementById('r');
const paper_div = document.getElementById('p');
const scissors_div = document.getElementById('s');

function getComputerChoice() {
  const choices = ['r', 'p', 's'];
  const randomNumber = (Math.floor(Math.random() * 3));
  return choices[randomNumber];
}

function convertToWord(letter) {
  if (letter === "r") return "Rock";
  if (letter === "p") return "Paper";
  return "Scissors";
}

function win(userChoice, computerChoice) {
  userScore++;
  userScore_span.innerHTML = userScore;
  computerScore_span.innerHTML = computerScore;
  const smallUserWord = "user".fontsize(3).sub();
  const smallCompWord = "comp".fontsize(3).sub();
  result_p.innerHTML = `${convertToWord(userChoice)}${smallUserWord} beats ${convertToWord(computerChoice)}${smallCompWord}. You win!`;
}

function lose(userChoice, computerChoice) {
  computerScore++;
  userScore_span.innerHTML = userScore;
  computerScore_span.innerHTML = computerScore;
  const smallUserWord = "user".fontsize(3).sub();
  const smallCompWord = "comp".fontsize(3).sub();
  result_p.innerHTML = `${convertToWord(userChoice)}${smallUserWord} loses to ${convertToWord(computerChoice)}${smallCompWord}. You lost!`;
}

function draw(userChoice, computerChoice) {
  const smallUserWord = "user".fontsize(3).sub();
  const smallCompWord = "comp".fontsize(3).sub();
  result_p.innerHTML = `${convertToWord(userChoice)}${smallUserWord} equals ${convertToWord(computerChoice)}${smallCompWord}. It's a draw`;
}

function game(userChoice) {
  const computerChoice = getComputerChoice();
  switch (userChoice + computerChoice) {
    case "rs":
    case "pr":
    case "sp":
      win(userChoice, computerChoice);
      break;
    case 'rp':
    case 'ps':
    case 'sr':
      lose(userChoice, computerChoice);
      break;
    case 'rr':
    case 'pp':
    case 'ss':
      draw(userChoice, computerChoice);
      break;
  }
}

function main() {
  rock_div.addEventListener('click', function() {
    game('r');
  })
  paper_div.addEventListener('click', function() {
    game('p');
  })
  scissors_div.addEventListener('click', function() {
    game('s');
  })
};

main();

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  background-color: #24272E;
  font-family: avenir;
}

header {
  background: white;
  padding: 20px;
}


/*header each one*/

header>h1 {
  color: #24272E;
  text-align: center;
}

.score-board {
  border: 3px solid white;
  border-radius: 4px;
  width: 200px;
  margin: 20px auto;
  /*20px (top/bottom) & center (left/right) */
  color: white;
  padding: 15px 20px;
  text-align: center;
  font-size: 46px;
  position: relative;
}

.badge {
  background: #E2584D;
  font-size: 14px;
  padding: 2px 10px;
}

#user-label {
  position: absolute;
  top: 30px;
  left: -25px;
}

#computer-label {
  position: absolute;
  top: 30px;
  right: -30px;
}

.result {
  font-size: 40px;
  color: white;
}

.result>p {
  text-align: center;
  font-weight: bold;
}

.choices {
  text-align: center;
  margin-top: 50px;
}

.choice {
  display: inline-block;
  border: 4px solid white;
  border-radius: 50%;
  padding: 10px;
  margin: 0 20px;
  transition: all 0.3s ease;
}

.choice:hover {
  cursor: pointer;
  background: darkblue;
}

img {
  height: 100px;
  width: 100px;
}

#action-message {
  text-align: center;
  color: white;
  font-weight: bold;
  font-size: 20px;
  margin-top: 20px
}

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <title>Rock Paper Scissors</title>
  <meta name="description" content="DESCRIPTION">
  <link rel="stylesheet" href="styles.css">

</head>

<body>
  <header>
    <h1>Rock Paper Scissors</h1>
  </header>
  <div class="score-board">
    <div id="user-label" class="badge">user</div>
    <div id="computer-label" class="badge">comp</div>
    <span idea="user-score">0</span>:<span idea="computer-score">0</span>
  </div>

  <div class="result">
    <p>Paper cover rock. You win!</p>
  </div>

  <div class="choices">
    <div class="choice" id="r">
      <img src="images/rock.png" alt="rock">
    </div>
    <div class="choice" id="p">
      <img src="images/paper.png" alt="paper">
    </div>
    <div class="choice" id="s">
      <img src="images/scissors.png" alt="scissors">
    </div>
  </div>

  <p id="action-message">Make your move</p>






</body>
<script src="app.js"></script>

</html>

Answer 1

Beside your typo idea= / id= ...
you could drastically minify your game logic and code by using indexes integers.

Game of integers

• Use data-* attribute for user buttons. The attributes should hold numerical values 0, 1, 2. On click, the value will represents the player choice.
• The AI should play numbers too: const AI = ~~(Math.random() * 3) // 0, 1, 2

Now that you know AI and Player both use integers (instead of strange letters combinations), you can store the Move names into an array const moves = ["Rock", "Paper", "Scissors"]; (where 0 is Rock... etc)

Rock Paper Scissors Logic

The game has three possible round resolutions, PL wins, AI wins, Draw. Let's convert those "human" values to integers, in the same order:

• 0 = PL win
• 1 = AI win
• 2 = Draw

Here's how to calculate those:

Draw

To calculate a Draw is the simplest. It's when both AI and PL integers are equal. Let's return 2

result = PL === AI ? 2

Player wins

To calculate Player win, simply increment AI choice by 1 and do a modulo 3. If the result of this operation is equal to player's choice, than Player must have won! Let's return 0

AI wins

Else, since our game has only 3 possible states, it's not a draw, and it's not a player win, than must be AI win! And let's return 1

const result = PL===AI ? 2 : (AI+1)%3 === PL? 0 : 1; // Possible results: 0, 1, 2

The cool thing in having a game result index based too is that now you can use also an array of messages like messages = ["You won!", "AI won", "it's a draw!", ] and get the desired message by the result index!. And bonus! You can also increment the score array values, 0 being the player's index and 1 being AIs!

const moves = ["Rock", "Paper", "Scissors"],
  messages  = ["You won!", "AI won", "It's a draw!"], // [PL, AI, draw]
  score     = [0, 0, 0],                              // [PL, AI, draw]
  EL = sel => document.querySelector(sel),
  EL_result  = EL("#result"),
  EL_PLScore = EL("#PLScore"),
  EL_AIScore = EL("#AIScore");

function game() {
  const PL = +this.dataset.playermove;  // Get dataset value as integer
  const AI = ~~(Math.random() * 3);     // All you need: 0, 1, 2
  const result = PL === AI ? 2 : (AI + 1) % 3 === PL ? 0 : 1; // 0=PLwins 1=AIwins 2=draw 

  score[result]++; // Increment PL or AI's score (Increments number of draws too ;) )
  EL_result.innerHTML = `You: ${moves[PL]}<br>AI: ${moves[AI]}<br>${messages[result]}`;
  EL_PLScore.textContent = score[0];
  EL_AIScore.textContent = score[1];
}

// EVENTS:
document.querySelectorAll("[data-playermove]")
  .forEach(el => el.addEventListener("click", game));

<button data-playermove="0">ROCK</button>
<button data-playermove="1">PAPER</button>
<button data-playermove="2">SCISSORS</button>

<br>

YOU | <span id="PLScore">0</span>:<span id="AIScore">0</span> | AI

<div id="result"></div>