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Description

Adds static typing to JavaScript to improve developer productivity and code quality.

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Flow

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

For a background on the project, please read this overview.

Contents

Requirements

Flow works with:

  • macOS
  • Linux (64-bit)
  • Windows (64-bit, 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 how to get started.

Using Flow's parser from JavaScript

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

Flow is written in OCaml (OCaml 4.07.1 is required).

  1. Install
    opam
    :
  1. 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.
  1. Initialize
    opam
    :
  opam init
  1. Install OCaml and Flow's dependencies:
  # from within this git checkout
  opam switch create . --deps-only -y
  1. Build the
    flow
    binary:
  eval $(opam env)
  make

This produces the

bin/flow
binary.
  1. Build
    flow.js
    (optional):
  opam install -y js_of_ocaml.3.4.0
  make js

This produces

bin/flow.js
.

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

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

License

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

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