Tic Tac Toe in the command line with NodeJS. Run with: node playtictactoe.js

gamelogic.js

module.exports = class TicTacToe {
  
  constructor() {
    this.board = [
      ["", "", ""],
      ["", "", ""],
      ["", "", ""]
    ];
    this.currentPlayer = "X";
    this.lastMove; // keep track of most recent move, for hasWon() check
  }


  // Alternate players X and O
  switchTurn() {
    this.currentPlayer = this.currentPlayer === "X" ? "O" : "X";
  }


  // Given a move object {row: 1, col: 0}, return true if that cell is open
  isCellFree(move) {
    return this.board[move.row][move.col] === ""; 
  }


  // Given a move object {row: 1, col: 0}, set that location on the board to contain the current player's symbol
  playerMove(move) {
    this.board[move.row][move.col] = this.currentPlayer; 
  }


  // Given the most recent move, check if that makes a win!
  hasWon(move) {

    // Concatenate current move's row and column and the 2 diagonals
    let possibleWins = [
      this.board[move.row][0] + this.board[move.row][1] + this.board[move.row][2],
      this.board[0][move.col] + this.board[1][move.col] + this.board[2][move.col],
      this.board[0][0] + this.board[1][1] + this.board[2][2],
      this.board[2][0] + this.board[1][1] + this.board[0][2]
    ];

    return possibleWins.some( (str) => str === "XXX" || str === "OOO");
  }

  isBoardFull() {
    // Return false as soon as a cell with "" value is found; otherwise, return true
    for (let row = 0; row < this.board.length; row++) {
      for (let col = 0; col < this.board[row].length; col++) {
        if (this.board[row][col] === "") return false
      }
    }
    return true;
  }


  // Display board in the console (for testing)
  log() {
    this.board.forEach( (row, index) => {
      console.log(row);
    }); 
  }

};

gamelogic.test.js

const TicTacToe = require('./gamelogic.js');

test("Game initialized", () => {
  const game = new TicTacToe();
  console.log("Initial board: ");
  game.log();
  console.log("Initial player: " + game.currentPlayer);
  return game.board && game.currentPlayer === "X";
});

test("switchTurn alternates X and O", () => {
  const game = new TicTacToe();
  console.log("Initial player: " + game.currentPlayer);
  
  game.switchTurn();
  console.log("Next player: " + game.currentPlayer);
  if (game.currentPlayer !== "O") return false;

  game.switchTurn();
  console.log("Next player: " + game.currentPlayer);
  return game.currentPlayer === "X";
});

test("playerMove updates board at {move} with currentPlayer", () => {
  const game = new TicTacToe();
  console.log("Initial board: ");
  game.log();
  console.log("Initial player: " + game.currentPlayer);

  let move = {row: 1, col: 0};
  console.log("Move: ", move);
  game.playerMove(move);
  game.log();
  if (game.board[1][0] !== "X") return false;

  game.switchTurn();
  console.log("Next player: " + game.currentPlayer);
  
  move = {row: 2, col: 2};
  console.log("Move: ", move);
  game.playerMove(move);
  game.log();
  return game.board[2][2] === "O";
});

test("top row of Xs win", () => {
  const game = new TicTacToe();
  console.log("Initial board: ");
  game.log();
  console.log("Initial player: " + game.currentPlayer);

  let hasWon = false;
  let moves = [
    {row: 0, col: 0},
    {row: 0, col: 1},
    {row: 0, col: 2}
  ];
  moves.forEach( (move) => {
    game.playerMove(move);
    game.log();
    hasWon = game.hasWon(move);
    console.log("hasWon: " + hasWon);
  });
  
  return hasWon; // should be true!
});

test("middle col of Os win", () => {
  const game = new TicTacToe();
  console.log("Initial board: ");
  game.log();
  game.switchTurn();
  console.log("Switch turn to player: " + game.currentPlayer);

  let hasWon = false;
  let moves = [
    {row: 0, col: 1},
    {row: 1, col: 1},
    {row: 2, col: 1}
  ];
  moves.forEach( (move) => {
    game.playerMove(move);
    game.log();
    hasWon = game.hasWon(move);
    console.log("hasWon: " + hasWon);
  });
  
  return hasWon; // should be true!
});

test("diagonal 1 of Xs win", () => {
  const game = new TicTacToe();
  console.log("Initial board: ");
  game.log();
  console.log("Initial player: " + game.currentPlayer);

  let hasWon = false;
  let moves = [
    {row: 0, col: 0},
    {row: 1, col: 1},
    {row: 2, col: 2}
  ];
  moves.forEach( (move) => {
    game.playerMove(move);
    game.log();
    hasWon = game.hasWon(move);
    console.log("hasWon: " + hasWon);
  });
  
  return hasWon; // should be true!
});

test("diagonal 2 of Os win", () => {
  const game = new TicTacToe();
  game.log();
  game.switchTurn();
  console.log("Switch turn to player: " + game.currentPlayer);

  let hasWon = false;
  let moves = [
    {row: 0, col: 2},
    {row: 1, col: 1},
    {row: 2, col: 0}
  ];
  moves.forEach( (move) => {
    game.playerMove(move);
    game.log();
    hasWon = game.hasWon(move);
    console.log("hasWon: " + hasWon);
  });
  
  return hasWon; // should be true!
});

test("stalemate: hasWon is false, isBoardFull is true", () => {
  const game = new TicTacToe();
  let hasWon = false;
  let isBoardFull = false;
  // Moves alternate between players:
  let moves = [
    {row: 0, col: 0},
    {row: 1, col: 1},
    {row: 1, col: 0},
    {row: 2, col: 0},
    {row: 0, col: 2},
    {row: 0, col: 1},
    {row: 2, col: 1},
    {row: 1, col: 2},
    {row: 2, col: 2}
  ];
  
  moves.forEach( (move) => {
    game.playerMove(move);
    // console.log("Move: ", move);
    // game.log();
    hasWon = game.hasWon(move);
    isBoardFull = game.isBoardFull();
    // console.log("hasWon: " + hasWon);
    // console.log("isBoardFull: " + isBoardFull);
    if (hasWon || isBoardFull) return false; // expect no win, board not full!
    game.switchTurn(); // this time, switch turns after each move!
  });
  
  console.log("hasWon: " + hasWon);
  console.log("isBoardFull: " + isBoardFull);
  game.log();
  return !hasWon && isBoardFull; // hasWon should be false, isBoardFull should be true!
});



// 5 sec testing library:
function test(description, testFunction) {
  console.log(description);
  console.log("---------------------------------");
  if (!testFunction()) {
    console.log("*********** FAIL! ***********"); 
  }
  console.log("======================================\n");
}

messages.js

// MESSAGES TO DISPLAY IN THE CONSOLE

exports.CELL_FULL = "Oops, that cell on the board is already taken! Please enter a valid move (Example: 0, 1): ";


exports.INVALID_MOVE = "Sorry, didn't understand that move! Please enter a row and column from 0 to 2, separated by a comma. (Example: 2,1): ";


exports.getNextMovePrompt = (currentPlayer) => `Player ${currentPlayer}, please enter your move: `;


exports.START_MSG = `
~ * ~ * ~ * ~ *   Let's play Tic Tac Toe!   * ~ * ~ * ~ * ~

This is a two-player game, so bring a friend and let's begin!

-------------------------------------------------
INSTRUCTIONS:

  - Choose your move by typing a row and column (0, 1 or 2) separated by a comma.
    Example: 0,2 or 1,1

  - Press the ENTER key to make your move.

(If you don't know how to play Tic Tac Toe, Google "Tic Tac Toe rules"!)
-------------------------------------------------

Player X starts!
Player X, please enter your first move:`;


exports.getWinMsg = (currentPlayer) => `
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\tPlayer ${currentPlayer} wins!!!!!  ᕕ( ᐛ )ᕗ
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's game over. GG! Run 'node playtictactoe.js' to play again.
`;


exports.STALEMATE_MSG = `
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\tIt's a stalemate! Nobody won!  ¯\\_(ツ)_/¯
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

That's game over. GG! Run 'node playtictactoe.js' to play again.
`;

playtictactoe.js

const TicTacToe = require('./gamelogic.js');
const messages = require('./messages.js');

const game = new TicTacToe();

process.stdin.setEncoding('utf8');

process.stdin.on('error', (error) => {
  console.log('error: ' + error);
});

// Handle each chunk of user input
// NOTE: Pretty sure there are edge cases here I'm not handling!
// TODO: Should probably use a module like readline or similar
process.stdin.on('data', updateGame);

// START THE GAME! Print initial instructions: 
console.log(messages.START_MSG);


function updateGame(data) {
  let input = data.toString().trim().toUpperCase();

  // Quit game early if requested:
  if (input === "QUIT") {
    process.exit();
  }

  // Parse and validate the user's move 
  let move = parseMove(input);

  if (move === false) {
    console.log(messages.INVALID_MOVE);
    return;
  }

  if (!game.isCellFree(move)) {
    console.log(messages.CELL_FULL);
    return;
  }

  // Update game board with valid move and display the board
  game.playerMove(move);
  game.log();

  // If somebody won, show msg and quit!
  if (game.hasWon(move)) {
    console.log(messages.getWinMsg(game.currentPlayer));
    process.exit();
    return;
  }

  // Stalemate if board is full but nobody won.
  // Show msg and quit!
  if (game.isBoardFull()) {
     console.log(messages.STALEMATE_MSG);
    process.exit();
    return;
  }

  // If game is still continuing, switch turns and prompt for next move:
  game.switchTurn();
  console.log(messages.getNextMovePrompt(game.currentPlayer));
}


// Given a string like "1,2" validate and return {row:1, col:2}
function parseMove(input) {
  // Input must be a number from 0 to 2
  let inputArray = input.split(",");
  let row = validateCoordinate(inputArray[0]);
  let col = validateCoordinate(inputArray[1]);

  if (row === false || col === false) return false;

  return {row: row, col: col};
}


// Row/col coordinates must be a number from 0 to 2
function validateCoordinate(num) {
  let coordinate = parseInt(num, 10);
  if (isNaN(coordinate) || coordinate < 0 || coordinate > 2) {
    return false;
  }
  return coordinate;
}