React Learning : Tutorial

tictactoe.js

//Code from https://reactjs.org/tutorial/tutorial.html

// class Square extends React.Component {
//   render() {
//     return (
//       <button className="square" onClick={ () => {this.props.onClick()} }>
//         { this.props.value }
//       </button>
//     );
//   }
// }

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,
    }
  }
  
  jumpTo(step) {
    //  React will update only the properties mentioned in setState method leaving the remaining state as is. 
    this.setState({
      stepNumber: step,
      xIsNext: (step % 2) === 0,
    })
  }
  
  handleClick(i) {
    const history = this.state.history.slice(0, this.state.stepNumber + 1);
    const current = history[history.length - 1];
    const sq = current.squares.slice();
    
    if (calcWinner(sq) || sq[i]) {
      return;
    }
    sq[i] = this.state.xIsNext ? 'X' : 'O';
    this.setState({
      history: history.concat({
        squares: sq,
      }),
      xIsNext: !this.state.xIsNext,
      stepNumber: history.length,
    })
  }
  
  render() {
    const history = this.state.history;
    const current = history[this.state.stepNumber];
    const winner = calcWinner(current.squares);
    
    const moves = history.map((step, move) => {
      const desc = move ? 'Go to move # ' + move
                        : 'Go to game start';
      return (
        <li key={move}>
          <button onClick={ () => this.jumpTo(move) }>{desc} </button>
         </li>
      )
    })
    
    const 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)}/>
        </div>
        <div className="game-info">
          <div>{winner ? '!!! Winner:' + winner : status}</div>
          <ol>{moves}</ol>
        </div>
      </div>
    );
  }
}

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

const root = ReactDOM.createRoot(document.getElementById("root"));
root.render(<Game />);


function calcWinner(squares) {
  const winningLines = [
    [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 < winningLines.length; i++) {
    const [a,b,c] = winningLines[i];
    if (squares[a] && squares[a] === squares[b] && squares[a] === squares[c]) {
      return squares[a];
    }
  }
  return null;
}