Developing Wordpress-Plugin: Problems with loading .js into head and HTML-Snippet as a Shortcode

Good evening,

I was asked to develope a wordpress plugin for a project I am currently involved in, since I normally do Graphics- and UX Design (CSS3) I am not that familiar with developing plugins for WP, although I've got quite some understanding of PHP. I've got the following code:

<?php
/**
* Plugin Name: ExpButton Wordpress Plugin
* Plugin URI: https://url.de
* Description: Ein Generator des Expbuttons
* Version: 0.1
* Author: Wilko Meyer
* Author URI: http://url.com
**/

/**
* Loading js into header
**/

function add_async($url)
{
    if (strpos($url, '#asyncload')===false)
        return $url;
    else if (is_admin())
        return str_replace('#asyncload', '', $url);
    else
        return str_replace('#asyncload', '', $url)."' async='async";
}
add_filter('clean_url', 'add_async', 11, 1);


function expertbuttonjs()
{
    // Loading the JS
    wp_register_script( 'custom-script', plugins_url( 'https://www.expert-button.de/js.js#asyncload', __FILE__ ), array( 'jquery', 'jquery-$
    wp_enqueue_script( 'custom-script' );
}
add_action( 'wp_enqueue_scripts', 'wptuts_scripts_with_the_lot' );

/**
*Creating Shortcode
**/

add_shortcode( 'shortcode', 'expbutton' );

function expbutton( $atts ) {

        /* Turn on buffering */
        ob_start(); ?>

        <div style="overflow:hidden;font-size:9px;height:auto;width:auto;text-align:center;margin:auto;" id="expertbuttonbg"><a target="_bl$

        <?php
    /* Get the buffered content into a var */
        $sc = ob_get_contents();

/**
*Expbutton to Shortcode
**/

add_shortcode( 'shortcode', 'expertbutton' );

function expertbutton( $atts ) {

        ob_start(); ?>

        <div style="overflow:hidden;font-size:9px;height:auto;width:auto;text-align:center;margin:auto;" id="expertbuttonbg"><a target="_bl$

        <?php

        $sc = ob_get_contents();

        ob_end_clean();

        /* Return the content as usual */
        return $sc;

}
?>

The purpose of this plugin is to load the js.js as async into the of the page and to create an shortcode from the HTML-Code below the /* Turn on buffering */ section which can be used at wordpress sites. Currently the code does not load the js into header and the shortcode which should be created does not work either and I have no Idea why. Hope someone can help me with this problem & has a clue why the plugin does not work. Thanks in advance!

• Wilko

via Chebli Mohamed