Discussion on: Better TypeScript... With JavaScript

[Pacharapol Withayasakpunt]

Now that I research, there seems to be a Babel plugin (tcomb) that can do $Refinement. You can do it side-by-side with Flow, and only use tcomb when you what to emit runtime type checking (e.g. function entry points.)

// @flow
import type { $Refinement } from 'tcomb'

const isInteger = n => n % 1 === 0
type Integer = number & $Refinement<typeof isInteger>;

function foo(n: Integer) {
  return n
}

foo(2)   // flow ok, tcomb ok
foo(2.1) // flow ok, tcomb throws [tcomb] Invalid value 2.1 supplied to n: Integer
foo('a') // flow throws, tcomb throws

In order to enable this feature add the tcomb definition file to the [libs] section of your .flowconfig.

gcanti / babel-plugin-tcomb

Babel plugin for static and runtime type checking using Flow and tcomb

It would probably throw error, if I try to use tcomb alongside TypeScript.