Flow

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.

Requirements

Flow works with:

• Mac OS X
• Linux (64-bit)

There are binary distributions for Mac OS X and many variants of Linux; you can also build it from source on almost any 64-bit Linux variant.

Installing Flow

Flow is simple to install: all you need is the flow binary on your PATH and you're good to go.

Using Homebrew

Installing Flow with Homebrew package manager:

brew install flow

To ensure you get the latest version of Flow, update your Homebrew with:

brew update

Using OPAM

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=4.01.0
opam install flowtype
eval `opam config env`
flow --help

Getting started

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.

Building Flow

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 OSX, 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.

Running the tests

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'

Join the Flow community

• Website: http://flowtype.org/
• irc: #flowtype on Freenode
• Twitter: follow @flowtype and #flowtype to keep up with the latest Flow news.

License

Flow is BSD-licensed. We also provide an additional patent grant.