2023-02-16 Frontend Working Group Meeting Minutes

Date

Feb 16, 2023

TBD

Time	Item	Presenter	Notes

Time

Item

Presenter

Notes

20 minutes

Loading external themes

tl;dr;

Paragon’s design tokens intends to compile its own theme CSS instead of MFEs needing to compile Paragon’s SCSS → CSS.
- It would result in core.css and light.css CSS files.
- See https://github.com/openedx/paragon/issues/2014 for more details.
Relies on 2 new config variables being present (potentially 3+ in the future):
- APP_THEME_CORE_URL (core theme CSS)
- APP_THEME_LIGHT_URL (CSS variable definitions specific to light theme variant)
- [in the future] APP_THEME_DARK_URL (CSS variables definitions specific to dark theme variant, one day)
Implements useAppTheme React hook to load/inject the external theme URLs into the HTML <head>.
Does not render MFE until the external CSS is loaded to avoid Flash of Unstyled Content (FoUC).
Ensures that once we do support more than 1 theme variant (i.e., both light and dark), switching between them does not introduce FoUC.
Provides a mechanism for consuming MFEs to (eventually) switch the theme at runtime by exposing a dispatch function and a set of reducer actions to mutate the app theme state (e.g., a consuming MFE could do dispatch(setAppThemeVariant('dark')) in the future once more theme variant(s) beyond "light" is supported.

Discuss:

What about versioning?
- For example, will the externally hosted CSS (e.g., on CDN) ever be incompatible with the version of Paragon installed in each individual MFE?
  - Should the externally hosted CSS be versioned in some way?
- Concerns around using an open source, versioned CDN that’s always in sync with published NPM versions?
  - For example, jsDelivr suggests they are
    ”production-ready” (docs).
  - Example CSS variables for the alpha release of Paragon hosted externally on jsDelivr: https://cdn.jsdelivr.net/npm/@edx/paragon@alpha/scss/core/css/variables.css
Local development?
- Currently, I have a Node.js Express API running locally with endpoints to serve the compiled core CSS and the light theme variant CSS from my local Paragon checkout.
- Need to explore options if there’s a way to point the config variables to CSS files from local checkout of Paragon without needing to serve them from a running Node.js Express API.
Alternatives to hosting compiled CSS on a CDN in our current MFE architecture?
- Brian Smith suggested possibly looking into https://github.com/overhangio/tutor-minio (S3-like object storage for Open edX) as possible alternative.

Update on MFE Domains

@Pedro Martello

7min

Ghassan

https://github.com/openedx/frontend-build/pull/266
I can present the diff of css between with and without the purge css plugin

git diff --no-index dist/app.4fce923d8a1007f74bd7.css dist-with/app.2abb1105ce90dd2f22da.css