Libraries to write unit tests that can be run in the browser or in node.js

Libraries used to display modals (popup windows) in web applications

Ecosystem around Astro project (the web site/app builder)

Utilities for forms: dropdown menus, slider...

Tools to create desktop apps

Libraries to display warning / error / success messages on web application pages

Web workers are a web API that allow you to run code in a separate thread (not to be mistaken with "Service workers"!)

Libraries to visualize hierarchical data as a tree (E.g.: file explorer)

Low levels libraries to handle keyboard events