index.js

class Note extends React.Component {
  constructor({age}) {
    super()
    // {age } = props.age
    // this.age =  {age}
    this.age = {age}
  }

  componentDidMount(){
  }

  render() {
    return (
      <div>
        <h1>{this.props.age}</h1>
      </div>
    )
  }
}


ReactDOM.render(
  <Note age={22}>
  </Note>,
  document.getElementById('root'),
)