title: TinyMCE wordpress, custom button does not show up
body: <p>I created a plugin in wordpress to add a button to the TinyMCE. I have at the moment the code below which follows very strictly the example here: 
  <a href="https://www.gavick.com/blog/wordpress-tinymce-custom-buttons#tc-section-1" rel="nofollow noreferrer">https://www.gavick.com/blog/wordpress-tinymce-custom-buttons#tc-section-1</a></p>
  
  <p><strong>Php file</strong></p>
  
  <pre><code>&lt; ? php
      /*
      Plugin Name: TinyMCE Custom Buttons
      Plugin URI:
      Description:
      Version:
      Author:
      Author URI:
      License:
      License URI:
      */
  
      //Hook the button on init, so after loading wordpress
      add_action('init', 'add_button1234');
  
      //add filters within th function which loads after loading wordpress
      function add_button1234() {
          // add new buttons
          add_filter('mce_buttons', 'myplugin_register_buttons1234');
          // Load the TinyMCE plugin 
          add_filter('mce_external_plugins', 'register_1234');
      }
  
  
      //Add the newly created button to ithe $buttons array
      function register_1234($buttons) {
          array_push($buttons, 'separator', 'button1234');
          return $buttons;
      }
  
      //create the button
      function myplugin_register_tinymce_javascript1234($plugin_array) {
          $plugin_array['button1234'] = plugins_url('plugin.js', __FILE__);
          return $plugin_array;
      }
  ?&gt;
  </code></pre>
  
  <p><strong>javascript file</strong></p>
  
  <pre><code>(function() {
      tinymce.PluginManager.add('button1234', function(editor, url) {
          editor.addButton('button1234', {
              text: 'My test button',
                  icon : false,
                  onclick : function() {
                  editor.insertContent('Hello World!');
              }
          });
      });
  })();
  </code></pre>
  
  <p>Also when I follow exactly the code from the site (only adapting the JS url, it doesn't work.) What could I possible have done wrong?</p>