[dgreensp]

I used both Flow and TypeScript extensively at my last job (coda.io), and through a series of thoughtful discussions and debates, we chose to migrate to TypeScript, even though we had already started using Flow in parts of our codebase.

Microsoft did a really good job putting resources behind TypeScript, making sure tooling and IDE integrations are good, and generally getting a ton of momentum going. TypeScript is fast-moving, with bugs fixed and features added at a high rate, and the quality of discussion on the issue tracker is high. Flow, in comparison, was not evolving as fast.

Flow touts global inference, which I think means better types when you don't necessarily have annotations on module boundaries, but I mostly care about what's possible in a greenfield or well-annotated codebase.

Flow deserves a ton of credit, and Microsoft probably studied it in detail, but I think the advantages are overblown at this point. Take the soundness thing. TypeScript added null-strictness a while ago, and recently they improved function type polymorphism. The reality is that both type systems have limits and you sometimes need to type something imperfectly or use an escape valve ("any"). In most cases, however, TypeScript gives you more sophisticated tools to construct the types you want, so you actually get better types. Maybe TypeScript lacks a theoretical underpinning for soundness, but there's no reason it can't continue to get "more and more sound," with it harder and harder to find good examples of unsoundness.

[agento]

I only post on HN about once a year. But I want to chime in on this topic.

At my current job we started a clean slate codebase (react/redux/webpack) beginning of 2016 and had everything typechecked by Flow from the start.

We found Flow to be extremely unreliable and cumbersome to use with not much apparent commitment behind it. As soon as Typescript hit 2.0 we converted the entire codebase (fairly easy to do since the syntax and semantics are very similar') and have been super happy with that decision.

I wholly agree on you remark about soundness vs. tooling. Flow tooling sucked, error messages were cryptic and unhelpful and we ran into obvious mistakes all the time that Flow did NOT catch, without being able to figure out why that was. Editor support was lacking and we just never trusted the typechecker.

Bolting on types to Javascript has tradeoffs and Microsoft did an amazing job of making the right tradeoffs.

There is noticeable effort and momentum behind the project that inspires a lot of confidence in the languages future. It has completely changed the way I write Javascript and I can't imagine going back to an untyped world.

That change was not in rock-solid confidence that TS catches all my errors (although it does a remarkably good job at that), but the sheer productivity improvement types enable (autocompletion, project-wide renaming, all that stuff users of Java or C# IDEs have available to them).

[AriaMinaei]

I advocated flow for two years, and I still find it interesting as a typesystem. But what finally led me to give up was the core team's lack of community engagement.

It's very difficult get the team's attention to a bug or a question. As a result, they fail to see the common pain points of actual users.

Typing higher order components is one common pain point that still doesn't have a clear solution. So, unless you're avoiding HOCs altogether, you can't really benefit from type annotations in your react codebase (you'll have too many implicit `any`s).

You'll find more of these common use cases that flow doesn't optimise for. They're all over the issues section. Unfortunately, issues on Github generally don't get much attention from the team either, so I'm guessing users sometimes give up on reporting them. This has happened to me quite a few times. I didn't report some bugs because putting together a reduced test case takes time, and that time would be wasted if your issue is not gonna be paid attention to.

What makes matters worse, is that there is no public roadmap. You don't know what the team's priorities are. You don't know when the bugs that affect your work are gonna get fixed, or some feature you need is gonna get implemented. You don't even know if it's on the radar.

Of course, the Flow team is under no obligation to do any of that. They have no obligation to fix bugs for us or publish a roadmap. I'm already grateful that they've given us access to their work and without charging money. However, they do have the responsibility to communicate what their priorities are. If they're positioning Flow as an alternative to TypeScript, which is a well-supported, community-oriented project, then they should state clearly that Flow simply isn't. Call it a research project, or a project focused on a single company's use cases. Don't ask people to bet their own projects on it, when they clearly shouldn't. It'll be a big loss of productivity for them down the line, and your messaging is partly responsible for that.

[_ar7]

Yeah I second this. Despite having a superior type system, flow is so behind in both tooling and 3rd party library definitions it's really hard to justify continuing to use it over typescript. It's weird to say, but the unsoundness of typescript doesn't matter much next to all the other advantages.

Besides, I feel like if I really want a strong type system https://reasonml.github.io/ might be the better choice over flow.

[hackits]

Flow/Typescript both of great but writing from start from scratch both flow and typescript slow me down with all the hassle of needing to define the types of parameters and data structures. Typescript being a bit verbose at time too.

When working with another person API then typescript does become a godsend in helping understand what the bloody hell does this callback parameter are required.

[dahauns]

>When working with another person API then typescript does become a godsend in helping understand what the bloody hell does this callback parameter are required.

Plot twist: While you are cursing at the person who wrote that API, you slowly realize that it was you all along.

[hackits]

Agree, typescript does help with that slow realization that its a problem with your code passing in undefined instead of a object.

[pjmlp]

Verbosity is quite helpful when doing maintenance on foreign code.

[oceanic]

Apologies, offtopic: wait, Coda.io only uncloaked less than a month ago and you've already left??

[AnkhMorporkian]

I mean, I've worked for several companies and left months before they actually launched. Any contractor who works with startups have been through similar situations.

Can't speak for OP's situation though.