Sign Up for Free

RunKit +

Try any Node.js package right in your browser

This is a playground to test code. It runs a full Node.js environment and already has all of npm’s 1,000,000+ packages pre-installed, including babel-plugin-transform-flow-to-gen with all npm packages installed. Try it out:

var babelPluginTransformFlowToGen = require("babel-plugin-transform-flow-to-gen")

This service is provided by RunKit and is not affiliated with npm, Inc or the package authors.

babel-plugin-transform-flow-to-gen v0.0.13

Turn flow definitions into generator functions

Flow to gen

Transforms flow type aliases into generators for property based testing


This Babel plugin attempts to alleviate the manual task of creating and maintaining fixtures/mocks by transforming all Flowtype type aliases into generator functions for mock data. Additionally, it provides a framework for automatically generating random input for typed functions and React components. If you're unfamiliar with generative or property based testing, please check out an implementation of Quickcheck in your language of choice. Also look at testcheck.js which is 100% compatible and wrapped by the runtime of this library.

By running this Babel transform on your code:

  • all type aliases are transformed in testcheck.js generators
  • all typed functions can immediately retrieve randomly generated inputs
  • all typed React components can immediately retrieve randomly generated props


  • handle TypeofTypeAnnotation
  • handle ExistentialTypeAnnotation
  • handle recursive types
  • handle Flow globally defined types
  • handle React components



Getting Started

babel-plugin-transform-flow-to-gen transforms your type aliases into functions that create testcheck.js generators.


import {sample, types} from 'babel-plugin-transform-flow-to-gen/api';

type Person<T> = {
  firstName: string,
  lastName: string,
  age: T

// use the generator static member to create samples
const personGen = Person(types.number());
sample(personGen, 20);
// [{
//   "firstName": "9OY3o",
//   "lastName": "fB",
//   "age": 0
// },
// {
//   "firstName": "8Hft5LwfK",
//   "lastName": "51Vnn54vb9xHO",
//   "age": 2
// },
// {
//   "firstName": "7i59Sr35GAJiv626uiV",
//   "lastName": "s7GIgEf",
//   "age": 3
// },
// {
//   "firstName": "Mys89F65i36n921",
//   "lastName": "",
//   "age": 1
// }, ...]

function setFirstName(person: Person<number>, firstName: string) {
  // ...

// returns an array of args for setFirstName
// [
//  [{
//   "firstName": "3o",
//   "lastName": "j467DA",
//   "age": 0
//   }, "f02j"]
// , ...]


yarn add babel-plugin-transform-flow-to-gen



RunKit is a free, in-browser JavaScript dev environment for prototyping Node.js code, with every npm package installed. Sign up to share your code.
Sign Up for Free