Getting Started with ReactJS

The instructions below can be followed to create a simple user interface in React.js. React.js is an open-source user interface library for JavaScript originated by Facebook.

These instructions are a simplified version of the tutorial found on React.js’s official website, currently available at the URL
“https://facebook.github.io/react/tutorial/tutorial.html”
.

TicTacToeViaReactJS.png

1. If you have not already done so, install Node.js. As of this writing, the latest version is available for download at the URL “https://nodejs.org/en/download/”.

2. In any convenient location, create a new directory named “ReactJS”.

3. Open a command prompt, navigate to the ReactJS directory created in the previous step, and run the following command to install the “create-react-app” utility:

	npm install -g create-react-app

4. Still in the command prompt, run the following commands and wait for them to complete. A new React.js application called “my-app” will be created within the ReactJS directory.

	create-react-app my-app
	cd my-app
	npm start

5. Navigate to the “src” directory within the newly created “my-app” directory.

6. Delete the existing contents of the src directory.

7. Still within the src directory, create a new text file named “index.css”, containing the following text.


/* 
 * This code is minimally adapted from a sample found at the URL
 * https://facebook.github.io/react/tutorial/tutorial.html 
 */

body {
  font: 14px "Century Gothic", Futura, sans-serif;
  margin: 20px;
}

ol, ul {
  padding-left: 30px;
}

.board-row:after {
  clear: both;
  content: "";
  display: table;
}

.status {
  margin-bottom: 10px;
}

.square {
  background: #fff;
  border: 1px solid #999;
  float: left;
  font-size: 24px;
  font-weight: bold;
  line-height: 34px;
  height: 34px;
  margin-right: -1px;
  margin-top: -1px;
  padding: 0;
  text-align: center;
  width: 34px;
}

.square:focus {
  outline: none;
}

.kbd-navigation .square:focus {
  background: #ddd;
}

.game {
  display: flex;
  flex-direction: row;
}

.game-info {
  margin-left: 20px;
}

8. Still within the src directory, create a new text file named “index.js”, containing the following text.


// This code is minimally adapted from a sample found at the URL
// https://facebook.github.io/react/tutorial/tutorial.html

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

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() {
    super();
    this.state = {
      history: [
        {
          squares: Array(9).fill(null)
        }
      ],
      stepNumber: 0,
      xIsNext: 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
    });
  }

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

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

    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>
      );
    });

    let status;
    if (winner) {
      status = "Winner: " + winner;
    } else {
      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>{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;
}

10. Back in the command prompt, navigate to the “my-app” directory and run the command “npm start” to start the application.

11. If it is not done automatically, open a web browser and navigate to the URL “http://localhost:3000”. Verify that a tic-tac-toe grid is displayed.

12. Click the “Game Start” link, then click on the various cells of the tic-tac-toe to play the game.

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