text: import React, { Component } from 'react';
  import Square from './square';
  import './board.css';
  
  class Board extends Component {
      constructor(props) {
          super(props);
  
          this.state = {
                          squares: Array(9).fill(null),
                          xIsNext: true,
                      }
          this.handleClick = this.handleClick.bind(this);
      }
  
      handleClick(i) {
          const squares = this.state.squares.slice();
          
          if (calculateWinner(squares) || this.state.squares.every((val) => {return val!==null})) {
              this.setState({squares: Array(9).fill(null), xIsNext: true});
              return;
          }
  
          if (squares[i] ) {
              return;
          }
  
          squares[i] = this.state.xIsNext ? 'X' : 'O';
          this.setState({squares: squares, xIsNext: !this.state.xIsNext});
      }
  
      renderSquare(i) {
          return <Square value={this.state.squares[i]}
                          onClick={()=> this.handleClick(i)}
                  />
      }
  
      render() {
          const winner = calculateWinner(this.state.squares);
          let status;
          if (winner) {
              status = 'Winner: ' + winner;
          } else {
              status = 'The next player: ' + (this.state.xIsNext ? 'X' : 'O');
          }
          return(
              <div className="game">
                  <div className="status">{status}</div>
                  <table className="board">
                      <tbody>
                      <tr className="board-row">
                          {this.renderSquare(0)}
                          {this.renderSquare(1)}
                          {this.renderSquare(2)}
                      </tr>
                      <tr className="board-row">
                          {this.renderSquare(3)}
                          {this.renderSquare(4)}
                          {this.renderSquare(5)}
                      </tr>
                      <tr className="board-row">
                          {this.renderSquare(6)}
                          {this.renderSquare(7)}
                          {this.renderSquare(8)}
                      </tr>
                      </tbody>
                  </table>
  
              </div>
          );
      }
  }
  
  export default Board;
  
  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;
    }