React tutorial: tic-tac-toe game (last edit 2018-01-12)

react-tic-tac-toe.js

// React tutorial: tic-tac-toe game
// https://reactjs.org/tutorial/tutorial.html
// https://davidfq.me/blog/react-first-steps/

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';

function Square(props) {
  return (
    <button className={`square ${props.className}`} onClick={props.onClick}>
      {props.value}
    </button>
  );
}

class Board extends React.Component {
  renderSquare(i) {
    const isWinnerPlay = (this.props.winner && 
      this.props.winner.sequence && 
      this.props.winner.sequence.indexOf(i) >= 0) ? 'is-winner' : ''
    return (
      <Square
        key={`square-${i}`}
        value={this.props.squares[i]}
        onClick={() => this.props.onClick(i)}
        className={isWinnerPlay}
      />
    );
  }
  render() {
    const rows = Array.from(Array(3).keys())
    const cols = Array.from(Array(3).keys())
    return (
      <div>
        {rows.map((row) => 
          <div key={`board-row-${row}`} className="board-row">
            {cols.map((col) => {
              const index = row === 0 ? col : (row * cols.length) + col;
              return this.renderSquare(index)
            })}
          </div>  
        )}
      </div>
    );
  }
}

class Game extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      history: [{
        squares: Array(9).fill(null),
        playIndex: null,
      }],
      stepNumber: 0,
      xIsNext: true,
      direction: 1, // as in SQL: ASC -> 1, DESC -> -1 
    };
  }
  handleClick(i) {
    const history = this.state.history.slice(0, this.state.stepNumber + 1);
    const current = history[history.length - 1];
    const squares = current.squares.slice();
    
    if (calculateWinner(squares) || squares[i]) {
      return;
    }    
    
    squares[i] = this.state.xIsNext ? 'X' : 'O';
    
    this.setState({
      history: history.concat([{
        squares: squares,
        playIndex: i,
      }]),
      stepNumber: history.length,
      xIsNext: !this.state.xIsNext,
    });
  }
  jumpTo(step) {
    this.setState({
      stepNumber: step,
      xIsNext: (step % 2) === 0,
    });
  }
  flipMoves() {
    this.setState({ direction: this.state.direction * -1 })
  }
  render() {
    const history = this.state.history.slice();
    const current = history[this.state.stepNumber];
    const winner = calculateWinner(current.squares);

    if (this.state.direction < 0) {
      history.reverse()
    }

    const moves = history.map((step, move) => {    
      move = this.state.direction < 0 ? (history.length - 1) - move : move
      
      let pos = ''
      
      if (step.playIndex !== null) {
        const quotient = Math.floor(step.playIndex / 3);
        const remainder = (step.playIndex + 1) % 3;
                
        const row = quotient + 1;        
        const col = remainder === 0 ? 3 : remainder;              
        
        pos = `(${row}, ${col})`;
      }

      const desc = move ?
        `Go to move #${move}` :
        'Go to game start';
      
      const className = this.state.stepNumber === move ? 'is-active' : ''
      return (
        <li key={desc} className={className}>
          <button onClick={() => this.jumpTo(move)}>{desc}</button> {pos}
        </li>
      );
    });

    let status;
    if (winner) {
      status = 'Winner: ' + winner.player;
    } else {
      status = 'Next player: ' + (this.state.xIsNext ? 'X' : 'O');
    }

    return (
      <div className="game">        
        <div className="game-board">
          <Board
            squares={current.squares}
            onClick={(i) => this.handleClick(i)}
            winner={winner}
           />
        </div>
        <div className="game-info">
          <div>{status}</div>
          <ol reversed={this.state.direction < 0}>{moves}</ol>
          <button onClick={() => this.flipMoves()}>flip moves</button>
        </div>
      </div>
    );
  }
}

function calculateWinner(squares) {
  const lines = [
    [0, 1, 2],
    [3, 4, 5],
    [6, 7, 8],
    [0, 3, 6],
    [1, 4, 7],
    [2, 5, 8],
    [0, 4, 8],
    [2, 4, 6],
  ];
  for (let i = 0; i < lines.length; i++) {
    const [a, b, c] = lines[i];
    if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
      return {
        player: squares[a],
        sequence: lines[i]
      }
    }
  }
  return null;
}

// ========================================

ReactDOM.render(
  <Game />,
  document.getElementById('root')
);