有两个玩家参与之后，就需要判断胜负，以及游戏何时结束。

在 Board.js 文件中添加 calculateWinner 方法来计算判断游戏，传入 squares 是一个长度为 9 的数组。

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]
  ]
  const len = lines.length
  for (let i = 0; i < len; i++) {
    const [a, b, c] = lines[i]
    if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
      return squares[a]
    }
  }
  return null
}

然后，修改 render 方法，在这里面调用 calculateWinner() 方法来判断是否玩家有胜出，如果有的话，就展示获胜消息。

  const winner = calculateWinner(this.state.squares)
    let status
    if (winner) {
      status = 'winner：' + winner
    } else {
      status = 'Next player:' + (this.state.isNext ? 'X' : 'O')
    }

每次点击格子都会触发 handleClick 事件，需要在这个事件里面调用 calculateWinner() 方法，如果有一方玩家已胜出，或者该 Square 已经被填充时，就不做处理直接返回了。

  handleClick (i) {
    const squares = this.state.squares.slice()
    if (calculateWinner(squares) || squares[i]) {
      return
    }
    squares[i] = this.state.isNext ? 'X' : 'O'
    this.setState(
      {
        squares: squares,
        isNext: !this.state.isNext
      }
    )
  }

实践一下效果：

完整代码如下：

import React, { Component } from 'react'
import Square from './Square'
class Board extends Component {
  constructor(props) {
    super(props)
    this.state = {
      squares: Array(9).fill(null),
      isNext: true
    }
  }
  handleClick (i) {
    const squares = this.state.squares.slice()
    if (calculateWinner(squares) || squares[i]) {
      return
    }
    squares[i] = this.state.isNext ? 'X' : 'O'
    this.setState(
      {
        squares: squares,
        isNext: !this.state.isNext
      }
    )
  }
  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 = 'Next player:' + (this.state.isNext ? 'X' : 'O')
    }
    return (
      <div>
        <div className="status">{status}</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>
    )
  }
}
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]
  ]
  const len = lines.length
  for (let i = 0; i < len; i++) {
    const [a, b, c] = lines[i]
    if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
      return squares[a]
    }
  }
  return null
}