Flow is a static typechecker for JavaScript. To find out more about Flow, check out flowtype.org.
For a background on the project, please read our launch blog post.
Flow works with:
- Mac OS X
- Linux (64-bit)
- Windows (64-bit)
There are binary distributions for each of these platforms and you can also build it from source on any of them as well.
Flow is simple to install: all you need is the flow binary on your PATH and you're good to go.
The recommended way to install Flow is via the flow-bin npm package. Adding flow-bin to your project's package.json:
- provides a smoother upgrade experience, since the correct version of Flow is automatically used based on the revision you check out
- installs Flow as part of your existing
npm installworkflow - lets you use different versions of Flow on different projects
npm install --save-dev flow-bin
node_modules/.bin/flow
Although not recommended, you can also install Flow globally (for example, perhaps you don't use npm or package.json).
The best way to install globally is via flow-bin:
npm install -g flow-bin
flow # make sure `npm bin -g` is on your path
On Mac OS X, you can install Flow via the Homebrew package manager:
brew update
brew install flow
You can also build and install Flow via the OCaml OPAM package manager. Since Flow has some non-OCaml dependencies, you need to use the depext package like so:
opam install depext
opam depext --install flowtype
If you don't have a new enough version of OCaml to compile Flow, you can also use OPAM to bootstrap a modern version. Install OPAM via the binary packages for your operating system and run:
opam init --comp=4.03.0
opam install flowtype
eval `opam config env`
flow --help
Getting started with flow is super easy.
- Initialize Flow by running the following command in the root of your project
flow init
- Add the following to the top of all the files you want to typecheck
/* @flow */- Run and see the magic happen
flow check
More thorough documentation and many examples can be found at http://flowtype.org.
Flow is written in OCaml (OCaml 4.01.0 or higher is required) and (on Linux) requires libelf. You can install OCaml on Mac OS X and Linux by following the instructions at ocaml.org.
For example, on Ubuntu 14.04 and similar systems:
sudo apt-get install ocaml libelf-dev
On OS X, using the brew package manager:
brew install ocaml ocamlbuild libelf opam
Once you have these dependencies, building Flow just requires running
make
This produces a bin folder containing the flow binary.
Note: at this time, the OCaml dependency prevents us from adding Flow to npm. Try flow-bin if you need a npm binary wrapper.
Flow can also compile its parser to JavaScript. Read how here.
While Flow is written in OCaml, its 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 (and should install flow-bin from npm above), but JavaScript packages which make use of parsing Flow-typed JavaScript can use this to generate Flow's syntax tree with annotated types attached.
To run the tests, first compile flow using make. Then run bash ./runtests.sh bin/flow
There is a make test target that compiles and runs tests.
To run a subset of the tests you can pass a second argument to the runtests.sh file.
For example: bash runtests.sh bin/flow class | grep -v 'SKIP'
- Website: http://flowtype.org/
- 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
Flow is BSD-licensed. We also provide an additional patent grant.