Reactチュートリアル　◯✖️ゲーム

##Reactで作る　◯✖️ゲーム

公式サイト 　　　https://ja.reactjs.org/tutorial/tutorial.html
公式の最終コード https://codepen.io/gaearon/pen/gWWZgR?editors=0010
###
変更するのは一つのファイル(index.js)だけ
デザインを変えたければindex.cssを変更する

```js:プロジェクトディレクトリ/src/index.js
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';

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

class Board extends React.Component {
  renderSquare(i) {
    return (
      <Square
        value={this.props.squares[i]}
        onClick={() => this.props.onClick(i)} 
      />
    );
  }

  render() {
    return (
      <div>
        <div className="board-row">
          {this.renderSquare(0)}
          {this.renderSquare(1)}
          {this.renderSquare(2)}
        </div>
        <div className="board-row">
          {this.renderSquare(3)}
          {this.renderSquare(4)}
          {this.renderSquare(5)}
        </div>
        <div className="board-row">
          {this.renderSquare(6)}
          {this.renderSquare(7)}
          {this.renderSquare(8)}
        </div>
      </div>
    );
  }
}

class Game extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      history: [{
        squares: Array(9).fill(null)
      }],
      stepNumber: 0,
      xIsNext: true,
    };
  }

  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' : '0';
    this.setState({
      history: history.concat([{
        squares: squares,
      }]),
      stepNumber: history.length,
      xIsNext: !this.state.xIsNext,
    });
  }

  jumpTo(step) {
    this.setState({
      stepNumber: step,
      xIsNext: (step % 2) === 0,
    });
  }

  render() {
    const history = this.state.history;
    const current = history[this.state.stepNumber];
    const winner = calculateWinner(current.squares);

    const moves = history.map((step, move) => {
      const desc = move ?
        '移動' + move :
        'ゲームスタート';
      return (
        <li key={move}>
          <button onClick={() => this.jumpTo(move)} >{desc}</button>
        </li>
      );
    });

    let status;
    if (winner) { 
      status = '勝者：' + winner;
    } else {
      status = '次のプレイヤー：'  
                     +
               (this.state.xIsNext ? 'X' : '0');
    }

    return (
      <div className="game">
        <div className="game-board">
          <Board
            squares={current.squares}
            onClick={(i) => this.handleClick(i)}
          />
        </div>
        <div className="game-info">
          <div>{ status }</div>
          <ol>{ moves }</ol>
        </div>
      </div>
    );
  }
}

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

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

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 squares[a];
    }
  }
  return null;
}

```
イメージ
<img width="270" alt="スクリーンショット 2020-04-30 17.30.46.png" src="https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/515025/980297c4-906f-3d4b-b1dc-817d0dbfed5c.png">
<img width="272" alt="スクリーンショット 2020-04-30 17.31.01.png" src="https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/515025/e42a4f9d-752b-b863-bfc8-b97f6d88928b.png">

ゲームスタートで新規ゲーム開始
ゲーム途中に移動ができる