flow-to-dts

Convert Flow libdefs to Typescript declaration files.

This tool is currently pre-alpha. Contribution of issues, suggesions, and pull requests are welcome!

Usage

Command Line

flow-to-dts input.flow.js output.d.ts

Node API

Transforming a code string:

import { transform } from 'flow-to-dts';

const input = 'type MyCode';

transform(input).then((output) => console.log(output));

Transforming an AST:

import { parse } from '@babel/parser';
import { transformAst } from 'flow-to-dts';

const input = parse('type MyCode');

transformAst(input).then((output) => console.log(JSON.stringify(output)));

Supported Features

(Note that this is not intended as an exhaustive list, but merely a representative sample indicating some of the key transformations performed by the tool.)

Feature	Supported	Flow	Typescript
Flow Header	✔️	// @flow	//
Module Exports	✔️	declare module.exports: MyModule;	export = MyModule;
Mixed Type	✔️	mixed	number | string | boolean | symbol | object
Nullable Types	✔️	?string	string | null | undefined
Tuple Types	✔️	[number, string]	[number, string]
Exact Objects	✔️	{| name: string |}	{ name: string }
Open Objects	✔️	{ name: string }	{ name: string; [field: string]: any }
Class Types	✔️	Class<SomeType>	typeof SomeType
Built-in Types	✔️	http$ClientRequest	import { ClientRequest } from "http";
Key Types	❌	$Keys<A>
Value Types	❌	$Values<A>
Difference Types	❌	$Diff<A>
Partial Types	✔️	$Shape<A>	Partial<A>
Rest Types	❌	$Rest<A>
Supertypes	❌	$Supertype<A>
Subtypes	❌	$Subtype<A>
Existential Type	✔️	*	any

Acknowledgements

Special thanks to the creators and maintainers of the following projects that made this tool possible:

• astexplorer
• babel
• babel-handbook
• babel-plugin-tester
• flow-cheatsheet
• flow-typed
• recast
• typescript-vs-flowtype
• yargs