react tutorial for beginners

1As far as I can tell from looking, codecademy, w3schools, 
2and many answers on stack overflow are all outdated.
3
4The best option is "https://reactjs.org/"

1import React from 'react';
2
3class App extends React.Component {
4   constructor(props) {
5      super(props);
6      
7      this.state = {
8         data: 'Initial data...'
9      }
10      this.updateState = this.updateState.bind(this);
11   };
12   updateState() {
13      this.setState({data: 'Data updated...'})
14   }
15   render() {
16      return (
17         <div>
18            <button onClick = {this.updateState}>CLICK</button>
19            <h4>{this.state.data}</h4>
20         </div>
21      );
22   }
23}
24export default App;

1class Board extends React.Component {
2  constructor(props) {    super(props);    this.state = {      squares: Array(9).fill(null),    };  }
3  renderSquare(i) {
4    return <Square value={i} />;
5  }

1npx create-react-app my-app
2cd my-app
3cd src
4
5# If you're using a Mac or Linux:
6rm -f *
7
8# Or, if you're on Windows:
9del *
10
11# Then, switch back to the project folder
12cd ..

1  renderSquare(i) {
2    return <Square value={i} />;
3  }

1class Board extends React.Component {
2  constructor(props) {   
3    super(props);  
4    this.state = {   
5      squares: Array(9).fill(null),
6    }; 
7  }
8  renderSquare(i) {
9    return <Square value={i} />;
10  }
11}