index.js

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


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

  jumpTo(step) {
    this.setState({
      stepNumber: step,
      xIsNext: (step % 2) ? false : 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' : 'O';
    this.setState({
      history: history.concat([{
        squares: squares
      }]),
      stepNumber: history.length,
      xIsNext: !this.state.xIsNext,
    });
  }

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

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

    const moves = history.map((step, move) => {
    const desc = move ?
      'Move #' + move :
      'Game start';
    return (
      <li key={move} >
        <a href="#" onClick={() => this.jumpTo(move)}>{desc}</a>
      </li>
    );
  });

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