Integrating TypeScript into expo start

[brentvatne]

https://twitter.com/natebosscher/status/1365023487451103239

it would be nice if expo start also ran type checking if your project was configured to use typescript.

I didn't realize that I had to run tsc separately to typecheck the entire project. My ide was type checking individual files, so I figured it was just working

[ntbosscher]

Also from our discussion:

• Would be nice if expo build and friends would fail when type checking fails
  • Should include an escape hatch, something like --ignore-typescript-errors

There might be something to learn from how create-react-app does things with typescript

[brentvatne]

i think people would basically all agree with that :)

[ntbosscher]

Ok, I'm good with that.

To be clear by console, I mean the spot where you ran the expo build / expo start command and the web console that pops up.

Anything we need to consider with that? Should we have a way to disable that functionality? What log level should ts errors be printed at?

[brentvatne]

what would be interesting for this feature is if it were built in such a way that the same infrastructure could be used to support other compile-to-js languages like reason. that said, typescript is the first-class supported language in the expo ecosystem, and so once we have that built we could enable typechecking in the expo server by default - but without blocking loading the application.

[brentvatne]

start, publish (which is run by build), and export could be good places to do this. it should definitely be possible to disable it, and we probably don't want to add any additional configuration to app.json - an env var could be a good approach.

[brentvatne]

another consideration - i think we would want to try this as something developers can opt-in to for a bit and see how that works before committing to making it the default for typescript apps