Hi,
If you'd like to write a WikiTree app or just play around with the WikiTree API, I implemented a Javascript library to make it easier to write code that gets data from WikiTree.
The code and documentation is here: https://github.com/PeWu/wikitree-js
The easiest way to experiment with the API is to open on online editor like StackBlitz.com or replit.com. You can find ready code examples that you can reuse in the wikitree-js readme.
You can use the library from Javascript code, no need to use Typescript. You can definitely use the library in an extension. If you use npm, you can simply npm install wikitree-js. I haven't tried using the library without npm.