React demo 01

const MyButton = (props) => {
    var handleOnClick = () => {};
    return(
    <button onClick={handleOnClick}>Counter {props.start}</button>
    // React.createElement("button", null, "Go")
  );
}

class Button extends React.Component{
    constructor(props){
    super(props);
    this.state = {counter: this.props.start};
  }

  handleOnClick = () => {
    this.setState((prevState) => {
        return {
            counter: prevState.counter + 1
    }});
  }

    render(){
    return (
        <div>
        <button onClick={this.handleOnClick}>
          Counter {this.props.start}</button>
        <div>{this.state.counter}</div>
      </div>
    );
  }
}

ReactDOM.render(<Button start={7} />, mountNode);