That's what I did. I switched to TypeScript after two years of being both heavily invested in Flow and advocating it.

The reason I initially chose Flow was the fact that their goals were more ambitious (trying to build a sound type system for example). And there were features that Flow had and TypeScript didn't (tagged unions for example).

The reason I ultimately switched to TypeScript was that after a couple of years, it had simply caught up and surpassed in the one area it was behind Flow (i.e. expressiveness of the type system and type-level programming), and that it had widened the lead in the areas that it was always better at, like much better tooling, bigger community, core team being more engaged with the community, releasing RCs to smooth out the rough edges, etc.

So yes, I switched to TypeScript, and I see that I'm spending less time working around the type system's quirks and more time getting things done. I'm also very much enjoying the fact that I can express types in TS that I never could in Flow. So my codebase has much better type coverage in TypeScript than it did with Flow.

[0] https://www.typescriptlang.org/docs/handbook/advanced-types....

> much better tooling

If you have the time, would you mind commenting specifically on this?

I'm using Flow, rather than TS, for a bunch of reasons you are probably familiar with, but over time I'm just wondering more and more if switching to TS might be worth it just for the tooling.

With Flow in VS Code (via the flow-for-vscode plugin), whilst things have slowly and steadily improved over the last 2 years it is still quite a way from 'just works'. I get the impression that the story for TS with VS Code is a lot different, and everything would just work out the box (intellisense, auto import, meaningful error messages tied to line numbers, etc) though I simply haven't yet found the justification to invest the time in migrating just to check this. If I'm wrong and it's the same or only very slightly better, it would obviously have been a time sink for not really much benefit.

Do you have any insights or advice on this? Even if you're not a VS Code user, what tools do you use that are better with TS than Flow?

Well, we had a 50K sloc codebase written in Flow. We had invested heavily in the type system for quality control, so we had types everywhere. This made it riskier for us to switch to another type system, which is why we stuck with Flow for longer than we should have.

The way I finally did it was that I tried out TS on a side-project that I wrote from scratch. I did expect better tooling with TS, but I was still surprised by how better the experience was.

Auto import just worked. Same with code navigation. And they made me work much faster. Intellisense was also much better. And the error messages more readable. (And they've gotten even better since)

All of these things work to some extent in flow+vscode, but the experience with TS was incomparably better.

I was still hesitant to switch the larger project to TS though, mainly because we were using some of Flow's more advanced features to type-check a function like `wrap()` in this code:

  const obj = {foo: true, bar: {baz: 2}}
  const wrappedObj = wrap(obj)
  wrappedObj.get('foo') // returns true
  wrappedObj.get('bar').set('baz', 'some string') // type error. baz must be a number

This was almost possible to do in Flow using `$ElementType<>` and `$Call<>`, but TS had no counterpart for `$Call<>`. Luckily though, TS soon came up with conditional types, which turned out to be a much more reliable way to handle these cases.

That's when I decided to switch the codebase to TS. It took about 5 days. It wasn't straightforward, but in the end, it gave us a much smoother developer experience.

If you're already using VS Code, I expect you'll find TypeScript support to be much, much nicer, since VS Code is the not-quite-official editor for TypeScript programming. VS Code is written in TypeScript, and I believe the TypeScript and VS Code teams (both at Microsoft) collaborate with each other to improve the developer experience of the two used in combination. For example, here are some TypeScript release notes showing the improvements to the TS language service and how they manifest in VS Code:

https://blogs.msdn.microsoft.com/typescript/2018/05/31/annou...

TypeScript has a nice architecture that provides a language service that can be used by any editor, but my impression is that VS Code is the "flagship" editor that gets these features first.

I personally use WebStorm, and I find its TypeScript support much better than its Flow support in various ways (though I haven't tried Flow in a while). Imports get added automatically, autocomplete is fast and has better results, navigation just works, etc. Part of this is historical: WebStorm supported TypeScript first, and was hesitant to support Flow during the long period of time when Flow didn't work on Windows. It now has Flow support, but I think it's just not as polished, and I don't see it come up as much in the release notes.

Yes.