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Flow is a static typechecker for JavaScript. To find out more about Flow, check outflow.org.

• Requirements
• Using Flow
• Using Flow's parser from JavaScript
• Building Flow from source
• Join the Flow community
• License

Flow works with:

• macOS (x86_64)
• Linux (x86_64 and arm64)
• Windows (x86_64, Windows 10 recommended)

There arebinary distributions for each of these platforms and you can also build it from source on any of them as well.

Check out theinstallation instructions, and thenthe usage docs.

While Flow is written in OCaml, its parser is available as a compiled-to-JavaScript module published to npm, namedflow-parser.Most end users of Flowwill not need to use this parser directly, but JavaScript packages which make use of parsingFlow-typed JavaScript can use this to generate Flow's syntax tree with annotated types attached.

Flow is written in OCaml (OCaml 5.2.0 is required).

1. Install system dependencies:

   • Mac:brew install opam

   • Debian:sudo apt-get install opam

   • Other Linux: seeopam docs

   • Windows:cygwin and a number of dependencies likemake,gcc andg++ are required.

     One way to install everything is to installChocolatey and then run.\scripts\windows\install_deps.ps1 and.\scripts\windows\install_opam.ps1. Otherwise, see the "Manual Installation" section ofOCaml for Windows docs and install all of the packages listed in ourinstall_deps.ps1.

     The remainder of these instructions should be run inside the Cygwin shell:C:\tools\cygwin\Cygwin. Thencd /cygdrive/c/Users/you/path/to/checkout.

2. Validate theopam version is2.x.x:

   opam --version

   The following instructions expect2.x.x. Should your package manager have installed a1.x.x version, please refer to theopam docs to install a newer version manually.

3. Initializeopam:

   # on Mac and Linux:opam init# on Windows:scripts/windows/init_opam.sh

4. Install Flow's OCaml dependencies:

   # from within this git checkoutmake deps

   note: If you find that you get an error looking forocaml-base-compiler version, your local dependency repo may be out of date and you need to runopam update +opam upgrade

5. Build theflow binary:

   eval$(opam env)make

   This produces thebin/flow binary.

6. Buildflow.js (optional):

   opam install -y js_of_ocaml.5.7.2make js

   This producesbin/flow.js.

   The Flow parser can also be compiled to JavaScript.Read how here.

To run the tests, first compile flow usingmake. Then runbash ./runtests.sh bin/flow

There is amake test target that compiles and runs tests.

To run a subset of the tests you can pass a second argument to theruntests.sh file.

For example:bash runtests.sh bin/flow class | grep -v 'SKIP'

• 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 theflowtype tag

Flow is MIT-licensed (LICENSE). Thewebsite anddocumentation are licensed under the Creative Commons Attribution 4.0 license (website/LICENSE-DOCUMENTATION).