Convert Flow-annotated files to TypeScript
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README.md

Flow-to-TypeScript Build Status npm mit

Compile Flow files to TypeScript

In Pre-Alpha - contributions welcome.

Installation

# Using Yarn:
yarn add flow-to-typescript

# Or, using NPM:
npm install flow-to-typescript --save

Usage

CLI

# Install globally
yarn global add flow-to-typescript

# Compile a file (all of these are equivalent)
flow2ts my/file.js.flow
flow2ts my/file.js.flow my/file.ts
flow2ts my/file.js.flow > my/file.ts
flow2ts -i my/file.js.flow -o my/file.ts
flow2ts --input my/file.js.flow --output my/file.ts

Programmatic

import { compile } from 'flow-to-typescript'
import { readFileSync, writeFileSync } from 'fs'

let path = 'path/to/file.js.flow'
let file = readFileSync(path, 'utf-8')

compile(file, path).then(ts =>
  writeFileSync('path/to/file.ts', ts)
)

TypeScript vs. Flow

Features

Done? Flow TypeScript
Maybe ?type (NullableTypeAnnotation) type | null | undefined
Null null null
Undefined typeof undefined undefined
Mixed mixed unknown
Void void void
Functions (A, B) => C (a: A, b: B) => C
Predicates (0) (a: A, b: B) => %checks (a: A, b: B) => C
Predicates (1) (a: A, b: B) => C %checks (a: A, b: B) => C
Exact types {| a: A |} { a: A }
Indexers { [A]: B } { [a: A]: B }
Opaque types opaque type A = B type A = B (not expressible)
Variance interface A { +b: B, -c: C } interface A { readonly b: B, c: C }
Bounds <A: string> <A extends string>
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>
Exact $Exact<A> A
Difference $Diff<A, B> TODO`
Rest $Rest<A, B> Exclude
Property type $PropertyType<T, k> T[k]
Element type $ElementType<T, K> T[k]
Dependent type $ObjMap<T, F> TODO
Mapped tuple $TupleMap<T, F> TODO
Return type $Call<F> ReturnType
Class Class<A> typeof A
Supertype $Supertype<A> any (warn - vote for https://github.com/Microsoft/TypeScript/issues/14520)
Subtype $Subtype<A> B extends A
Existential type * any (warn - vote for https://github.com/Microsoft/TypeScript/issues/14466)

Done

⚔ Babylon doesn't support it (yet)