# flow-to-ts

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Convert Flow code to TypeScript.

The goal of this project is to provide a tool that can translate 95% of Flow 
to TypeScript while maintaining a high percentage of the existing type 
information.  We don't want to convert code and end up with everything using
`any`.  We also want to avoid having to make a lot of manual changes to files
afterwards, e.g. changing `SyntheticEvent` to `React.Event`.

# Quick start

- `yarn global add @khanacademy/flow-to-ts`
- `flow-to-ts [options] <file globs>`

# Playground

https://flow-to-ts.netlify.com

# Principles

- when exact translation isn't possible:
  - downgrade to `any` when possible and provide a gentle warning
  - when it isn't possible to downgrade (e.g. `%checks`), remove the syntax
    and provide a forceful warning that the code in question will need a human
    to convert it manually.
- best effort to maintain blank lines and the position comments, this isn't
  always possible so warn in those situations where we can't, e.g. converting
  object type spreads to intersection types.

# Contibuting

## Bugs

Bug reports for converting Flow to TypeScript should include a link to the
playground with an example of a minimal reproducible example of the bug.

## Feature Requests

Feature requests are welcome.

## Pull Requests

Please make sure there is a GitHub issue first before creating a pull request
except for small things.  Also, please sign our [Contributor License Agreement](https://docs.google.com/forms/d/e/1FAIpQLSdyXYrc8ogVoA46J9KXyIj5nKlZzNkOnQG-4A1R7X_BWGTShQ/viewform).

Pull requests that fix a bug in the conversion code should include one or more
test cases and should have 100% diff coverage.

## Dev quick start

- `git clone git@github.com:Khan/flow-to-ts.git`
- `cd flow-to-ts`
- `yarn`
- `yarn test`

## Helpful resources

- https://github.com/niieani/typescript-vs-flowtype
- https://astexplorer.net/