With every new major version release of our popular CMS, we have some points of attention to bring to our developers and users. With the upcoming Joomla 4 launch, this is no different. You can load any UI framework you want in your extension, template, plugin, ... But you may not unload any media of the package (Bootstrap, jQuery, MooTools, Chosen, or whatever libraries are being introduced into 4.0), otherwise things will break.

Joomla's UI layer is not coupled to a single framework, the Joomla application does not arbitrarily load any media. But some extensions explicitly load media or libraries, and when you arbitrarily unload any of those used media or libraries, you’re asking for problems with the result that functionality will break.

What about the Joomla 4 templates?

The current backend template (not to be confused with the one previewed in the magazine which is still work in progress) is a Bootstrap 4 based template and requires all Bootstrap dependencies.
The frontend template shipping with 4.0 is a Bootstrap 4 based template with some customizations and as such the template requires all Bootstrap dependencies.

To be crystal clear here, these are TEMPLATE LEVEL DEPENDENCIES. This does not mean that Joomla 4 requires these technologies, only that the default templates (and inherently what most extension layouts will probably be designed against) are built this way. The use of the override systems will enable the use of any frontend framework.

The facts

Let’s state the facts :

• As of Alpha 2, the Joomla 4 backend template (Atum) is a Bootstrap 4 based template. (Note that at this point we cannot confirm any other dependencies, as soon as we have more information on this we will communicate this.)
• The Joomla 4 frontend template (Cassiopeia) is a Bootstrap 4 based template
• The default templates (to include the default extension layouts, as those are essentially designed against the default templates) are the ONLY part of Joomla coupled to a specific framework as it relates to UI elements; the use of system overrides will allow template builders to use any framework of their preference.
• Joomla 4 will ship with Bootstrap 4 and jQuery 3, but they will not be required elements when using core functionality (some overrides may be necessary, especially for UI components, but the JavaScript API is explicitly being rewritten to not be dependent on jQuery)

Most important

You can load any UI framework you want, but keep in mind, do not unload any media or libraries. Thank you!