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README.md Copy Chapter

Flow

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

Contents Copy Chapter

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

Requirements Copy Chapter

Flow works with:

* macOS (x86_64)
* 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 Copy Chapter

Check out the installation instructions, and then the usage docs.

Using Flow's parser from JavaScript Copy Chapter

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, 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 Copy Chapter

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: see opam docs
- Windows: cygwin and a number of dependencies like make, gcc and g++ are required.

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

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

2. Validate the opam version is 2.x.x:

opam --version

The following instructions expect 2.x.x. Should your package manager have installed a 1.x.x version, please refer to the opam docs to install a newer version manually.

3. Initialize opam:

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

4. Install Flow's OCaml dependencies:

# from within this git checkout
    make deps

note: If you find that you get an error looking for ocaml-base-compiler version, your local dependency repo may be out of date and you need to run opam update + opam upgrade

5. Build the flow binary:

eval $(opam env)
    make

This produces the bin/flow binary.

6. Build flow.js (optional):

opam install -y js_of_ocaml.5.7.2
    make js

This produces bin/flow.js.

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

Running the tests Copy Chapter

See tests/README.md for detailed testing documentation.

Join the Flow community Copy Chapter

License Copy Chapter