flow

# Flow
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Flow is a static typechecker for JavaScript. To find out more about Flow, check out [flow.org](https://flow.org/).

## Contents

- [Requirements](#requirements)
- [Using Flow](#using-flow)
- [Using Flow's parser from JavaScript](#using-flows-parser-from-javascript)
- [Building Flow from source](#building-flow-from-source)
- [Join the Flow community](#join-the-flow-community)
- [License](#license)


## Requirements

Flow works with:

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

There are [binary distributions](https://github.com/meta/flow/releases) 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](https://flow.org/en/docs/getting-started/#toc-installation), and then [the usage docs](https://flow.org/en/docs/getting-started/#toc-usage).

## Using Flow's parser from JavaScript

Flow's parser is available as a compiled-to-JavaScript module published to npm, named [flow-parser](https://www.npmjs.com/package/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 Rust. GitHub CI builds Flow from the `rust_port` workspace with nightly Rust.

1. Install system dependencies:

    - Install [Rust via rustup](https://rustup.rs/).
    - Install the nightly Rust toolchain:

      ```sh
      rustup toolchain install nightly
      ```

2. Build the Rust workspace:

    ```sh
    cd rust_port
    cargo +nightly build
    ```

3. Run the Rust tests:

    ```sh
    cargo +nightly test
    ```

4. Build an optimized `flow` binary:

    ```sh
    cargo +nightly build --release --bin flow_cli
    ```

5. Build `flow.js` (optional):

    The `flow.js` build also uses the Rust port. Install Emscripten, Node, Yarn, and a Rust nightly toolcha