Add TypeScript Support

[maneetgoyal]

Any plans for adding types?

[domoritz]

See #274

[jheer]

Yes, I would like to add types! I think my preferred route is not to port to TypeScript, but rather provide type files included along side the JavaScript source files. (Similar to how Observable Plot does this.)

[domoritz]

Can't wait for https://tc39.es/proposal-type-annotations/. 🙏

[maneetgoyal]

Yes, I would like to add types! I think my preferred route is not to port to TypeScript, but rather provide type files included along side the JavaScript source files. (Similar to how Observable Plot does this.)

Yeah, makes sense. Can avoid/defer a rewrite/migration to TS.

[domoritz]

https://github.com/NiGhTTraX/ts-monorepo seems like a good solution to supporting typescript in a monorepo (without the need to rebuild everything to get the latest changes in downstream packages).

[domoritz]

#355 gets us pretty close so I'll close this for now.

[domoritz]

We still have a lot of places without types.

[willium]

I think an underrated reason to port to TypeScript is that it could make contributing back to Mosaic easier for the uninitiated like myself. Currently, reading the code involves jumping between a lot of files, and reasoning about how variables are mutated, wrapped, and unwrapped at different points.