App.js

import React, { Component } from 'react';
import PropTypes from 'prop-types';

class App extends Component {
    render() {
        return (
            <div className="container">
                <div className="row">
                    <div className="col-md-12">
                        {this.props.message}
                    </div>
                </div>
            </div>
        );
    }
}

App.propTypes = {
    message: PropTypes.string.isRequired,
};

export default App;