I want to add a simple custom button to CKEditor in Drupal 8. So far I followed the Instructions [here][1] and [here][2], and my custom button is showing up on the configuration page under *Configuration > Content authoring > Text formats and editors*, where I added it to the *Basic HTML* and *Full HTML* presets.

[![my custom button is added to Basic HTML toolbars][3]][3]

However, when I want to create a new article, the button is not being shown in the editor toolbar.

[![my custom button is missing in node creation][4]][4]

I can verify by JS console outputs that my plugin **is** being loaded by CKEditor, and the `init` function actually runs. The button just does not appear. I appreciate any pointers. I have seen [this question, where somebody seems to have a similar problem][5], but I don't really understand the accepted answer as it seems to be specific to CKEditor templates.

I have not implemented any hooks in my module.

**info.yml of my module**

    name: Glossarion
    type: module
    description: >
      Some description. I'll think about it later.
    core: 8.x
    version: 0.1
    package: CKEditor
    dependencies:
      -ckeditor

**.php of my Drupal plugin**
    
    class Glossarion extends PluginBase implements CKEditorPluginInterface, CKEditorPluginButtonsInterface {

    public function getDependencies(Editor $editor) { return array(); }
    public function getLibraries(Editor $editor) { return array(); }
    public function isInternal() { return FALSE; }
    public function getConfig(Editor $editor) { return array(); }
    public function isEnabled(Editor $editor) { return TRUE; }

    public function getFile() {
      return drupal_get_path('module', 'glossarion') . '/js/plugins/glossarion/plugin.js';
    }

    public function getButtons() {
      return [
        'glossarion' => [
          'label' => t('Insert a Word from Glossarion'),
          'image' => drupal_get_path('module', 'glossarion') . '/js/plugins/glossarion/icons/glossarion-editor-icon.png',
          'command' => 'insertTimestamp'
        ]
      ];
    }
    }

**.js of my CKEditor Plugin**

    'use strict';
    
    CKEDITOR.plugins.add('glossarion',{
      icons: 'glossarion-editor-icon', // %REMOVE_LINE_CORE%
      init : function( editor ) {
        console.log("Glossarion init is being called");
        editor.addCommand( 'insertTimestamp', {
            exec: function( editor ) {
                var now = new Date();
                editor.insertHtml( 'The current date and time is: <em>' + now.toString() + '</em>' );
            }
        });
        // do I have to add the button here again? Seems to have no effect
        editor.ui.addButton( 'Timestamp', {
            label: 'Insert Timestamp',
            command: 'insertTimestamp',
            toolbar: 'basicstyles,0'
        });
        console.debug(editor);
      }
    });


  [1]: http://ckeditor.com/slides/ckeditor-in-drupal-8/#/
  [2]: http://alexcoder.info/en/content/dobavlenie-plagina-ckeditor-v-drupal-8
  [3]: https://i.sstatic.net/LxPG6.png
  [4]: https://i.sstatic.net/KhIdA.png
  [5]: http://drupal.stackexchange.com/questions/139075/implementing-ckeditors-plugin-in-drupal-8