@esmbly/transformer-flow

Transform Flow files to TypeScript.

Installation

# Using Yarn:
yarn add @esmbly/transformer-flow

# Or, using NPM:
npm install @esmbly/transformer-flow --save

Getting Started

Check out Using the Flow transformer guide for a step-by-step guide on how to get started with @esmbly/transformer-flow and the command-line interface.

Try

Try it out in the Esmbly version of WebAssembly Studio!

Usage

The @esmbly/transformer-flow transforms Flow files to TypeScript. In order to use it, make sure you have @esmbly/cli installed .

The following Esmbly configuration will transform all JavaScript files located in the src directory and output TypeScript files to the dist directory.

// esmbly.config.js

const Flow = require('@esmbly/transformer-flow');

module.exports = {
  input: ['./src/**/*.js'],
  transformers: [
    Flow.createTransformer(),
  ],
  output: [
    {
      format: '.ts',
      outDir: 'dist',
      rootDir: 'src',
    },
  ],
};

Configuration

The createTransformer() method accepts an optional configuration object (see the FlowTransformerOptions interface). The following options are possible.

Option	Description	Type	Default
removeFlowFlags (optional)	Whether or not to remove any // @flow comments	boolean	true
customRules (optional)	An object containing any custom rules which should be applied (existing rules can be overridden). Check out the custom-rule example for further details.	CustomRules

Examples

• Yarn/lockfile: Transforming a subset of yarn from Flow to TypeScript.
• Add: Transforming a simple Flow program to WebAssembly by chaining @esmbly/transformer-flow and @esmbly/transformer-wasm.
• Pad: Transforming a string pad program to WebAssembly by chaining @esmbly/transformer-flow and @esmbly/transformer-wasm.
• Custom Rule: Extending @esmbly/transformer-flow with a custom rule.
• Browser Example: Using esmbly and @esmbly/transformer-flow in the browser using Webpack.

Status

Supported?		Flow	TypeScript
✅	Primitive Types	boolean | number | string | null | undefined	boolean | number | string | null | undefined
✅	Void	void	undefined
✅	Literal Types	type Two = 2;	type Two = 2;
✅	Mixed Types	mixed	unknown
✅	Any Types	any	any
✅	Maybe Types	?type	type | null | undefined
✅	Function Types	(str: string) => boolean	(str: string) => boolean
❌	Function Shorthand	(A, B) => C	(a: A, b: B) => C
❌	Predicate Functions	(a: A, b: B) => C %checks	(a: A, b: B) => C
✅	Object Types	{ foo: boolean }	{ foo: boolean }
✅	Exact object types	{| a: A |}	{ a: A }
✅	Indexers	{ [A]: B }	{ [a: A]: B }
✅	Array Types	Array<string>, string[]	Array<string>, string[]
✅	Tuple Types	type A = [number, boolean]	type A = [number, boolean]
✅	Class Types
✅	Opaque types	opaque type A = B	type A = B (not expressible)
✅	Interface Types
✅	Variance	interface A { +b: B, -c: C }	interface A { readonly b: B, c: C }
✅	Generic Types
❌	Bounds	<A: string>	<A extends string>
✅	Union Types	number | boolean	number | boolean
❓	Disjoint unions
✅	Intersection Types	A & B	A & B
❓	Typeof types
✅	Typeof undefined	typeof undefined	undefined
✅	Type Casting	(a: A)	(a as A)
✅	Import default type	import type A from './b'	import A from './b'
✅	Import named type	import type { A } from './b'	import { A } from './b'

Utilities

Done?		Flow	TypeScript
✅	Keys	$Keys<A>	keyof A
❌	Values	$Values<A>	A[keyof A]
✅	ReadOnly	$ReadOnly<A>	Readonly<A>
✅	ReadOnlyArray	$ReadOnlyArray<A>	ReadonlyArray<A>
✅	Exact	$Exact<A>	A
❌	Difference	$Diff<A, B>	?
❌	Rest	$Rest<A, B>	?
❌	Property type	$PropertyType<T, k>	T[k]
❌	Element type	$ElementType<T, K>	T[k]
❌	Element type	$NonMaybeType<T>	NonNullable<T> (strictNullChecks)
❌	ObjMap	$ObjMap<T, F>	?
❌	ObjMapi	$ObjMapi<T, F>	?
❌	TupleMap	$TupleMap<T, F>	?
❌	Call	$Call<F>	ReturnType
❌	Class	Class<A>	typeof A
❌	Shape	Shape<T>	Partial<T>
❌	Supertype	$Supertype<A>	any (deprecated)
❌	Subtype	$Subtype<A>	B extends A (deprecated)
❌	Existential type	*	any (deprecated)

✅ Done
❌ Not implemented yet
❓ Status not known

Contributing

All types of contributions are very much welcome. Check out our Contributing Guide for instructions on how to get started.

Credits

@esmbly/transformer-flow is a customization/extension of the flow-to-typescript project ( ❤️) which is released under the following MIT license.

Copyright 2017 Boris Cherny <[e-mail]> 

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.