Title:
[Bug] Theme crashes on Discourse 2026.4.0-latest — Could not find module 'ember-this-fallback/js-component'
Description:
After updating Discourse to v2026.4.0-latest (commit 19374472fd), the FKB Pro theme causes a fatal frontend crash, making the forum partially unusable. Discourse shows the orange banner:
“由于主题/组件有错误，您的站点可能无法正常运行。由 ‘FKB Pro theme’ 引起。”
(Translation: “Due to an error in the theme/component, your site may not work properly. Caused by ‘FKB Pro theme’.”)
Root Cause:
The theme (or one of its components) still references the ember-this-fallback/js-component module, which has been removed from Discourse core in recent versions. This module was a compatibility shim for the deprecated Ember this-property-fallback pattern, which allowed templates to use {{foo}} instead of {{this.foo}}. Discourse officially announced the removal of this shim and required all themes/plugins to migrate to explicit this. bindings.
Error from browser console:
Failed to load theme 4 from https://www.sitetalk.net/...
Error: Could not find module 'ember-this-fallback/js-component' imported from (require)
[THEME 4 'FKB Pro theme'] Error: Could not find module 'ember-this-fallback/js-component' imported from (require)
at vendor.js
at requireModule (vendor.js)
at Object.lookup (chunk.js)
...
at reportThemeError (chunk.js)
(Discourse version shown in console: v2026.4.0-latest, Ember v6.10.1)
Environment:
| Item | Value |
|---|---|
| Discourse version | v2026.4.0-latest (commit 19374472fd) |
| Ember version | v6.10.1 |
| Theme | FKB Pro (default install from this repo) |
| Reproduction | 100% reproducible after upgrading Discourse |
We hope that the developers can fix this issue. Thanks!!!