reactapp.php

<?php

/*
Plugin Name: Dallas React App
Plugin URI:  http://link to your plugin homepage
Description: Create a basic React app
Version:     1.0
Author:      Giannis Dallas
Author URI:  https://giannisdallas.com
License:     GPL2 etc
License URI: 
*/

//[foobar]
function foobar_func( $atts ){
	return "<div id='reactApp'>This is a test</div>";
}
add_shortcode( 'foobar', 'foobar_func' );

function reactapp_enqueue_scripts() {
	wp_enqueue_script( 'React-js', 'https://unpkg.com/react@16/umd/react.production.min.js', array(), '', true  );
	wp_enqueue_script( 'React-DOM', 'https://unpkg.com/react-dom@16/umd/react-dom.production.min.js', array(), '', true  );

	wp_enqueue_script( 'custom-react-app', plugin_dir_url( __FILE__ ) . '/compiled/app.js', array(), '', true ); 
}

add_action( 'wp_enqueue_scripts', 'reactapp_enqueue_scripts' );