zadanie00.jsx

import React from 'react';
import ReactDOM from 'react-dom';

document.addEventListener('DOMContentLoaded', function(){
    class MyCheckbox extends React.Component {
        constructor(props){
            super(props);

            this.state = {
                isOn : false,
            };
        }
        handleChangeClick = () => {
            this.setState({
                isOn : ! this.state.isOn
            });
        }
        render(){
            return <div>
                <button onClick={this.handleChangeClick}>
                    { this.state.isOn ? 'TAK' : 'NIE' }
                    </button>
            </div>;
        }
    }

    class App extends React.Component {
        render(){
            return <MyCheckbox />;
        }
    }

    ReactDOM.render(
        <App />,
        document.getElementById('app')
    );
});