What I REALLY want to know is... can it run "flow" (https://github.com/facebook/flow). Because it's very useful yet painful to install... And I don't even know if it works on Windows.
In Compile OCaml to JavaScript, Run on Nodemeta
flow
Rust2014–2026
meta / flow
flow
Adds static typing to JavaScript to improve developer productivity and code quality.
55Distinct people
64Mentions
1Explicit recommenders
22.3KGitHub stars
What to know before exploring
What it is
Adds static typing to JavaScript to improve developer productivity and code quality.
GitHub
Where it is used
No documented product use was verified in the last source check.
What people are saying
I'm using Flow but I'd recommend TypeScript. I love Flow but TypeScript just seems to be more seriously maintained and less buggy. I've been waiting some bug fixes for 2 years…
ggregoire used a recommendation phrase. 2 indexed comments match. This is a phrase match, not a verdict.
No classified warning is attached to this page. Read the discussions before treating silence as approval.
Also in these discussions
- microsoft/typescript · linked in 7 of the same discussions
- meta/infer · linked in 3 of the same discussions
- reasonml/reason · linked in 3 of the same discussions
Mentioned in the same Hacker News threads. That is not proof they are substitutes.
This week on Hacker News
Nov 8–Nov 15 UTC · Direct repository links and separately labeled related project stories. Indexed through 11/15/2026, 4:01:40 AM UTC.
No direct repository links were found in the indexed HN discussions over the past seven days. Older discussions are available below.
Mentions over time
HN mentions by year64 dated mentions
Observed mentions: 2014-11-18 18:29:48 UTC to 2026-06-07 04:00:52 UTC.
* An incomplete calendar period is marked with an outlined bar. Its count is not directly comparable with a full period.
Counts come from the repository’s dated source evidence. Index cutoff: 2026-11-02 08:16:59 UTC.
View mention counts and date ranges
| Period | Start (UTC) | End (exclusive, UTC) | Mentions | Submissions | Comments |
|---|---|---|---|---|---|
| 2014 | 2014-01-01 00:00:00 UTC | 2015-01-01 00:00:00 UTC | 5 | 0 | 5 |
| 2015 | 2015-01-01 00:00:00 UTC | 2016-01-01 00:00:00 UTC | 13 | 0 | 13 |
| 2016 | 2016-01-01 00:00:00 UTC | 2017-01-01 00:00:00 UTC | 11 | 1 | 10 |
| 2017 | 2017-01-01 00:00:00 UTC | 2018-01-01 00:00:00 UTC | 10 | 2 | 8 |
| 2018 | 2018-01-01 00:00:00 UTC | 2019-01-01 00:00:00 UTC | 9 | 0 | 9 |
| 2019 | 2019-01-01 00:00:00 UTC | 2020-01-01 00:00:00 UTC | 6 | 0 | 6 |
| 2020 | 2020-01-01 00:00:00 UTC | 2021-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2021 | 2021-01-01 00:00:00 UTC | 2022-01-01 00:00:00 UTC | 1 | 0 | 1 |
| 2022 | 2022-01-01 00:00:00 UTC | 2023-01-01 00:00:00 UTC | 0 | 0 | 0 |
| 2023 | 2023-01-01 00:00:00 UTC | 2024-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2024 | 2024-01-01 00:00:00 UTC | 2025-01-01 00:00:00 UTC | 2 | 0 | 2 |
| 2025 | 2025-01-01 00:00:00 UTC | 2026-01-01 00:00:00 UTC | 2 | 1 | 1 |
| 2026 (partial) | 2026-01-01 00:00:00 UTC | 2027-01-01 00:00:00 UTC | 2 | 2 | 0 |
From the project README
An excerpt from the repository, fetched Nov 13, 2026.
Read the project’s introduction
Flow
Flow is a static typechecker for JavaScript. To find out more about Flow, check out flow.org.
Contents
Requirements
Using Flow
Using Flow's parser from JavaScript
Building Flow from source
Join the Flow community
License
Requirements
Flow works with:
macOS (arm64)
Linux (x86_64 and arm64)
Windows (x86_64, Windows 10 recommended)
There are binary distributions for each of these platforms and you can also build it from source on any of them as well.
Using Flow
Check out the installation instructions, and then the usage docs.
Using Flow's parser from JavaScript
Flow's parser is available as a compiled-to-JavaScript module published to npm, named flow-parser. Most end users of Flow
will not need to use this parser directly, but JavaScript packages which make use of parsing
Flow-typed JavaScript can use this to generate Flow's syntax tree with annotated types attached.
Building Flow from source
Flow is written in Rust. GitHub CI builds Flow from the rust_port workspace with nightly Rust.
Install system dependencies:
Install Rust via rustup.
Install the nightly Rust toolchain:
rustup toolchain install nightly
Build the Rust workspace:
cd rust_port
cargo +nightly build
Run the Rust tests:
cargo +nightly test
Build an optimized flow binary:
cargo +nightly build --release --bin flow_cli
Build flow.js (optional):
The flow.js build also uses the Rust port. Install Emscripten, Node, Yarn, and a Rust nightly toolchain with the wasm32-unknown-emscripten target and rust-src component first. GitHub CI uses Emscripten 3.1.44 and nightly Rust for this build.
rustup toolchain install nightly-2026-04-14 --target wasm32-unknown-emscripten --component rust-src
RUSTUP_TOOLCHAIN=nightly-2026-04-14 make js FLOW_JS_IMPL=rust-wasm
This produces bin/flow.js.
To build a faster, larger local development version instead, run:
RUSTUP_TOOLCHAIN=nightly-2026-04-14 make js FLOW_JS_IMPL=rust-wasm FLOW_DOT_JS_WASM_PROFILE=dev
The Flow parser can also be compiled to JavaScript. Read how here.
Running the tests
See tests/README.md for detailed testing documentation.
Join the Flow community
Website: https://flow.org
Discord: https://discord.gg/8ezwRUK
irc: #flowtype on Freenode
Twitter: follow @flowtype and #flowtype to keep up with the latest Flow news.
Stack Overflow: Ask a question with the flowtype tag
License
Flow is MIT-licensed (LICENSE). The website and documentation are licensed under the Creative Commons Attribution 4.0 license (website/LICENSE-DOCUMENTATION).
Read the full README on GitHubWhat Hacker News says
13 sourcessimilar :
Mozilla "Mentor Bugs
If you are looking for a bug with guidance, we maintain a set of bugs that are marked with an assigned mentor (see "Whiteboard" field). The mentor will help you get the necessary information to understand the issue, point out relevant parts of the code to look at, etc. You can browse these bugs on Bugs Ahoy!, but here's a list of unassigned mentor bugs to get you started:"
https://wiki.mozilla.org/Mobile/Get_Involved#Mentor_Bugs
Other examples:
#easyfix: https://github.com/facebook/flow/labels/easyfix
#beginner: https://github.com/eslint/eslint/labels/beginner
#exp:beginner https://github.com/docker/docker/issues?q=is%3Aopen+is%3Aiss...
In First Timers OnlyWe've been using Flow at Streak. Compared to my last experience with TypeScript, it's been really great for how easy it is to add into an existing codebase. Nothing about our build process had to change because we were already using Babel (which by default strips out Flow types and supports JSX) with Browserify. Flow understands node-isms and follows how commonjs and es6 modules include each other, and only enforces its type checking on files that have opted in with the magic /* @flow */ comment, so we didn't have to stop the world and make everything play nice with it in one go. We're gradually opting in more of our codebase over time. Its type system maps to javascript really well, supporting things like optional types, disjoint unions, intersection types, and polymorphic functions and classes.
The annoying things with Flow: No Windows
Read the rest
support yet which is the one thing holding me back from transitioning some personal projects over, but it sounds like progress is coming there[1]. There doesn't yet seem to be any real plans for letting 3rd party NPM modules bundle their own type definitions and have them be automatically used[2]. (Flow doesn't have issues with untyped imports at least. They're just treated as the any type.) Editor integration is pretty bad still. There's an Atom plugin, but it's buggy. This doesn't affect me too much as the "flow" command for type checking is quick to use (on the first run, it starts a long-running daemon in the background which watches your whole project for changes and keeps their type information cached) in the terminal I already always have open for interacting with git.
[1]: https://github.com/facebook/flow/issues/6
[2]: https://github.com/facebook/flow/issues/593
If you are using ES6 class syntax, then I would think you would also be using const / let; and if you are using const / let, then FlowTypes is, for me anyway, borderline unusable because it still does not support them (although there is apparently a fork with pseudo-support, if you want to deal with that):
https://github.com/facebook/flow/pull/431
In React.Component vs. React.createClassI'd like to try flow but it isn't available yet on windows [1] so it's not even an option for me (I'm on windows and I like to keep my things multi-platform friendly if possible). At the moment I'm using babel in Atom and typescript in VisualStudio.
[1] https://github.com/facebook/flow/issues/6
In Announcing TypeScript 1.5They use the Spidermonkey AST, but the parser is written with OCaml https://github.com/facebook/flow/blob/master/src/parser/pars... and the Lexer is generated with OCamllex, since there is support for compiling OCaml bytecode to Javascript it still runs in the Browser.
In Google Dart Will Not Be the Next Default Programming Language of the WebYes, it is called static analysis http://en.wikipedia.org/wiki/Static_program_analysis.
It exists for JavaScript:
https://github.com/sinelaw/infernu
https://github.com/facebook/flow
In Introducing T3: Enabling Large Scale JavaScript ApplicationsI'm also a fan of namespacing variants, and I used it extensively on an OCaml representation of the SpiderMonkey AST. (Coincidentally, up until writing our own parser we were using pfff's JavaScript parser! Go pfff!). Anyway, here are some other useful things I found in OCaml along the way:
Without namespacing, you might be using mutually recursive type definitions like
type statement = ExpressionStatement of expression
and expression = FunctionExpression of statement list
to do this with modules you need to use recursive modules, like
module rec Statement : sig
type t = Expression of Expression.t
end = struct
type t = Expression of Expression.t
end
and Expression : sig
type t = Function of Statement.t list
end = struct
type t = Function of Statement.t list
end
One of the sucky things about recursive mod
Read the rest
ules is that you cannot omit the signatures, however if your modules only include types then there is a shortcut that looks like
module rec Statement : sig
type t = Expression of Expression.t
end = Statement
and Expression : sig
type t = Function of Statement.t list
end = Expression
Links:
Big real world example:
https://github.com/facebook/flow/blob/3a5b4040b7d2a648f97a06...
Recursive module docs:
http://caml.inria.fr/pub/docs/manual-ocaml-400/manual021.htm...
Facebook made flow https://github.com/facebook/flow and TypeScript has already been mentioned
In Wallaby.js – An intelligent test runner that continuously runs your testsIf something might return null -- feel free to make a PR with making it a Maybe type, like here:
https://github.com/facebook/flow/blob/master/lib/dom.js#L359
In Angular 2: Built on TypeScript> What do you mean it's not possible to work around libraries and APIs returning nulls? That's exactly the point I made, Flow solved it.
Sorry, I had the really stupid misconception that Maybe Types could not be applied to libraries and browser APIs.
So it seems like a good start, but it doesn't seem really useful if they aren't even in the basic API's descriptions: https://github.com/facebook/flow/blob/master/lib/dom.js#L198
In Angular 2: Built on TypeScriptShould I learn oCaml instead ? Looks appealing because companies like Facebook are using it create tools like Flow ( https://github.com/facebook/flow ).
In Learn You a Haskell for Great Good (2008)> seen some truly awful TS code (mainly where the devs want to pretend the web doesn't exist)
I agree. Typescript is an impressive project, but most of the Typescript code I see looks more like C# or Java than Javascript. Sadly, it seems to have been created to accommodate that kind of approach.
But there's a lot to be said for strong and static typing when dealing with large projects.
That's why I'm hopeful for Flow, Facebook's new project to add static typing to Javascript:
https://github.com/facebook/flow
In React v0.13.0 Beta 1