reactjs-tutorial-tictactoe/src/index.js

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

/*TODO
    Rewrite Board to use two loops to make the squares instead of hardcoding them.
    Add a toggle button that lets you sort the moves in either ascending or descending order.
    When someone wins, highlight the three squares that caused the win.
    When no one wins, display a message about the result being a draw.
*/

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.handleClick(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),
            }],
            xIsNext: true,
            currentMoveIndex: 0,
        }
    }

    playTurn(i) {
        const history = this.state.history.slice(0, this.state.currentMoveIndex + 1);
        const currentState = history[history.length - 1];
        if (currentState.squares[i] || calculateWinner(currentState.squares)) {
            return;
        }

        const newSquares = [...currentState.squares];
        newSquares[i] = this.state.xIsNext ? 'X' : 'O';

        const playPosition = squareIndexToPosition(i);
        this.setState({
            history: [...history, {
                squares: newSquares,
                playX: playPosition[0],
                playY: playPosition[1],
            }],
            xIsNext: !this.state.xIsNext,
            currentMoveIndex: history.length,
        });
    }

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

    render() {
        const history = this.state.history;
        const currentState = history[this.state.currentMoveIndex];
        let status;
        const winner = calculateWinner(currentState.squares);
        if (winner) {
            status = `Winner: ${winner}`;
        } else {
            const nextPlayer = this.state.xIsNext ? 'X' : 'O';
            status = `Next player ${nextPlayer}`;
        }

        const moves = history.map((state, index) => {
            const description = index === 0 ?
                'Go to game start' :
                `Go to move #${index} [${state.playX}, ${state.playY}]`;
            return (
                <li key={index} className={index === this.state.currentMoveIndex ? 'selected' : null}>
                    <button onClick={() => this.jumpTo(index)}>{description}</button>
                </li>
            );
        });

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

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;
}

function squareIndexToPosition(index){
    return [
        index % 3,
        Math.floor(index / 3),
    ];
}

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

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