Problem/Motivation

After upgrading from Drupal 10.5.8 to 10.6.5, the CKEditor5 Font module stops working and prevents the CKEditor from initializing.
In the console of a node creation page, the following error is displayed:
TypeError: e is not a function
addStyleProcessorRule ckeditor5-dll.js

Steps to reproduce

1. Install Drupal 10.6.5 (which includes CKEditor5 47.6.0)
2. Install and enable `ckeditor_font` module (version 2.0.0-beta5)
3. Configure a text format to use Font plugins (Font Size, Font Family, Font Color, Font Background Color)
4. Navigate to a node add/edit form (e.g., `/node/add/page`)
5. Open browser console
6. Note that the CKEditor is not been displayed on the node form.

Expected behavior

CKEditor should initialize normally with font options available in the toolbar.

Actual behavior

- CKEditor does not initialize
- JavaScript error in browser console:

CommentFileSizeAuthor
Captura de tela de 2026-04-07 09-01-11.png140.21 KBgustavogmc

Comments

gustavogmc created an issue. See original summary.

marcoscano’s picture

marcoscano
Primary language Portuguese, Brazil
Location Barcelona, Spain
commented
Component: User interface » Code
Priority: Normal » Critical

Confirming this issue with the same root error after upgrading Drupal core 10.5.8 → 10.6.5 (CKEditor5 47.6.0). The OP reported it on ckeditor_font 2.0.0-beta5; I can confirm 2.0.0-beta6 (released 2025-06-29) is also affected, so it doesn't appear to have been
fixed by the latest beta.

Environment
- Drupal core 10.6.5
- CKEditor5 47.6.0 (bundled in core)
- ckeditor_font 2.0.0-beta6
- Affected toolbar items: fontColor and fontBackgroundColor. Removing them from a format's toolbar restores CKEditor5; including either one prevents the editor from initializing on that format.

Browser console stack trace 

  TypeError: e is not a function                                                                                                                                                                                                                                     
      at Os.addStyleProcessorRules (ckeditor5-dll.js?v=47.6.0:5:393288)                                                                                                                                                                                              
      at new Y (font.js?te52l4:5:21529)                                                                                                                                                                                                                              
      at ckeditor5-dll.js?v=47.6.0:5:169256                                                                                                                                                                                                                          
      at Array.map (<anonymous>)                                                                                                                                                                                                                                     
      at ckeditor5-dll.js?v=47.6.0:5:169205                                                                                                                                                                                                                          
      at d.init (ckeditor5-dll.js?v=47.6.0:5:169281)
      at w.initPlugins (ckeditor5-dll.js?v=47.6.0:5:183237)                                                                                                                                                                                                          
      at editor-classic.js?v=47.6.0:4:11097                                                                                                                                                                                                                          
      at new Promise (<anonymous>)                                                                                                                                                                                                                                   
      at w.create (editor-classic.js?v=47.6.0:4:11055)

The font.js?te52l4 frame is from web/modules/contrib/ckeditor_font/js/ckeditor5_plugins/ckeditor5-font/build/font.js. Looks like the bundled plugin is calling DataSchema.addStyleProcessorRules(name, callback) with a non-function as the second argument, which
CKEditor5 47 enforces (where earlier versions tolerated it).

Side effect worth flagging for anyone hitting this

Because the editor fails to initialize, the textarea also fails to round-trip values cleanly on submit when the field uses a format whose toolbar contains these items — saved content can come back empty after the form re-loads. So the impact is more than just
a missing toolbar; it's effectively data loss for end users until the format is patched. Bumping this to critical due to the potential data loss.

** AI Disclaimer: **

This troubleshooting has been done with the help of Claude Code. The comment above has been drafted by CC, and reviewed by me.

tiagoz’s picture

tiagoz
Primary language Portuguese, Portugal
commented

I suggest you to install https://www.drupal.org/project/ckeditor5_plugin_pack and the fonts pack as a substitute of this.