ESNext Tic Tac Toe

tic-tac-toe.js

/* global require process */

const readline = require('readline');
const log = console.log;

class TicTacToe {

  static get combos() {
    return [
      // rows
      [0, 1, 2], [3, 4, 5], [6, 7, 8],
      // cols
      [0, 3, 6], [1, 4, 7], [2, 5, 8],
      // diag
      [0, 4, 8], [2, 4, 6]
    ];
  }

  static get symbols() { return {player1: 'X', player2: 'O'}; }

  constructor(readline) {
    this.rl = readline;
    this.board = [1,2,3,4,5,6,7,8,9];
    this.currentPlayer = 'player2';
    this.onNext();
  }

  get symbol() { return TicTacToe.symbols[this.currentPlayer]; }

  checkValidCell(input) {
    return typeof this.board[input - 1] === 'number';
  }

  checkWin() {
    const board = this.board;
    const combos = TicTacToe.combos;

    for (let combo of combos) {
      let total = 0;

      for (let cell of combo) {
        // skip to next combo
        if (board[cell] !== this.symbol) { break; }
        total++;

        if (total === 3) { return true; }
      }
    }

    return false;
  }

  displayBoard() {
    const board = this.board;
    const len = board.length;
    let s = '';

    for (let i = 1; i <= len; i++) {
      s += i % 3 !== 0 ?
        // all cells that are not end of row cells should end with '|'
        (board[i - 1] + '|') :
        // between each row insert long dash line break, except for last row
        i === 9 ? board[i - 1] : (board[i - 1] + `\n\u2014 \u2014 \u2014\n`);
    }

    log(`\n${s}\n`);
  }

  onNext(input) {
    input = this.processInput(input);

    // input is 'undefined' when game starts
    if (input !== undefined) {
      if (input === -1 || !this.checkValidCell(input)) {
        log('invalid input or cell already in use. try again.');
        this.rl.setPrompt(`${this.currentPlayer}: `);
        this.rl.prompt();

        return;
      }

      this.setBoard(input);

      if (this.checkWin()) {
        this.displayBoard();
        log(`${this.currentPlayer} wins!`);
        process.exit(0);
      }
    }

    this.displayBoard();
    this.currentPlayer = this.currentPlayer === 'player1' ? 'player2' : 'player1';
    this.rl.setPrompt(`${this.currentPlayer}: `);
    this.rl.prompt();
  }

  processInput(input) {
    if (input === undefined) { return; }

    input = Number.parseInt(input.trim().charAt(0));

    if (Number.isNaN(input) || input === 0) { return -1; }

    return input;
  }

  setBoard(input) {
    this.board[input - 1] = TicTacToe.symbols[this.currentPlayer];
  }
}

const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout
});
const game = new TicTacToe(rl);

rl.on('line', input => game.onNext(input));