react framework tutorial code example

Example 1: react tutorial

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

Example 2: react tutorial

As far as I can tell from looking, codecademy, w3schools, 
and many answers on stack overflow are all outdated.

The best option is "https://reactjs.org/"

Example 3: react quick tutorial

ReactDOM.render(  
    <Hello />,   
    document.getElementById("root")  
);