Khan Academy (KA) is a very large website developed by a very small team, and there are often aspects of the site that need updates.
The KA Extension is a community project to create a browser extension to improve on KA. It fixes bugs and adds small features, mostly in the computer science area of the site. The KA Extension has been used by more than 4,000 people to improve their KA experience.
The KA Extension is written in Typescript. (Fun fact: I originally learned TypeScript to contribute to the KA Extension.)
Since KA is a React-based site, DOM modifications we made would frequently be undone by React, and KA's source was minified. These types of hurdles made developing the extension difficult, but gave me practice writing code for "hostile" environments.
The KA Extension is open source on Github.
KA Extension on Github