[RFC] Move to Typescript

[HenriBeck]

With more OS projects now planning to move to Typescript (jest, Vue.js, etc.), I think it would be time to think about doing the same. Typescript has matured and now with eslint and babel both supporting Typescript as well, it should be future proof.

Additionally, I think the tooling around Typescript (speed, autocompletion), etc. is far head of flow currently.

I would start with "rewriting" smaller packages (like css-functions and theming) in the beginning.
Also, I started writing the new docs with Typescript.

Are you willing to implement it?
Yes

EDIT: I started rewriting the core in my fork in Typescript as an experiment.

[TrySound]

Besides better tooling I saw a lot of unsoundness in TS which is "won't fix" when flow to gonna be and actually already safer than TS in some cases. For me it doesn't worth to switch.
I'm quite happy with flow in big project and open source.

[HenriBeck]

Why would Typescript be less type-safe?

[TrySound]

Here guys from flow team provides some examples
https://discord.gg/zGY9gW

For example TypeScript doesn't have exact types at all (microsoft/TypeScript#12936) when flow is gonna have them by default. Object spread is unsound (microsoft/TypeScript#15454) when flow is already more sound here and is gonna improve experience with exact by default.

[TrySound]

Flow has some problems but flow team is quite active and open last few weeks. They are going to the right direction but their plan is time consuming. Now they have resources to work with community.

[kof]

That's interesting, do you know how many people work on flow full time? I feel like flow with strict mode and better error descriptions would actually make the whole thing quite competitive. It's just a matter if companies are willing to invest enough to improve.

[TrySound]

This is just now. There are more people there

[kof]

Fulltime contributors? Where do you see it?

[TrySound]

It's a chat with flow team (facebook guys). The link I put above.

[HenriBeck]

I think flow error descriptions and reporting is quite better (especially when it comes to react props) than Typescripts.

What I now dislike the most about it is how slow the editor integration is and that types are an afterthought.

[TrySound]

Which editor do you use?

[HenriBeck]

Webstorm, and for me the autocompletion, auto-import etc. is really slow, I think in a recent release they improved the language server to handle request while they are recomputing all of the types though.

[TrySound]

There is one representative from webstrom team in flow chat. They are discussing better integration. Yeah, main problem is checking too much. Ignoring things usually helps.

[HenriBeck]

The reason why I proposed this change that a lot of quite large projects are moving into this direction.
And yeah, TS maybe is sometimes unsafer, but I think this only applies for certain type definitions/operators.

The reason I got to like Typescript so much is that the language was designed with types in mind and not just an afterthought/addition like flow.

[TrySound]

Well, sorry, but herd instinct is a bad reason to refactor all the project. It looks like "flow is a shit and nobody will ever use, let's kill it". By doing this you just add fuel to the fire of hate which is really started by just one person.

By the way about big projects decisions. Here's another one
https://github.com/mdn/mdn/pull/53/files#diff-992ca475abeb0c101165f19ff62d37e7R14