Oscar Franco

Strip flow types to read flowtype file from vanilla JS

August 2023

Unlike Typescript where you have tools like ts-node that allow you to quickly run typescript files without tooling (think without webpack or metro), I found however no way to achieve this with FlowType.

I needed to use a translation file that had flow types in vanilla JS and I figured out a way to strip the types.

Install flow remove types package

yarn add flow-remove-types

Use flow remove types

In my use case I had a huge file with translations that is strongly typed and I wanted to migrate them to another format.

The process is basically:

  1. Read file from disk
  2. Pass it to flow-remove-types
  3. Write to another file (or you can also load it in memory with another package require-from-string)
  4. import it normally

Here is a part of the script I used:

// allows you to call this file like a script from the command line
#!/usr/bin/env node

let flowRemoveTypes = require('flow-remove-types');
// let translations = require('../src/I18n/translations') // cannot import it bc it contains flow types
let fs = require('fs');

function unpackTranslation(translationObj, key) {
  if(translationObj[key]) {
    return translationObj[key]

  const res = {}
  Object.entries(translationObj).forEach(entry => {
    res[entry[0]] = unpackTranslation(entry[1], key)

  return res


// Start by taking the translations file and stripping flow out of it
let translationsInput = fs.readFileSync('../src/I18n/translations.js', 'utf8');

// Remove flow and module export with traditional syntax
let translationsOutput = flowRemoveTypes(translationsInput).toString().replace('export default TRANSLATIONS', 'module.exports = TRANSLATIONS')

fs.writeFileSync('./translations.js', translationsOutput);

// then we can just read this file
const translations = require('./translations');

let languages = ['en', 'it', 'pt', 'fr', 'es', 'de']
let keys = JSON.parse(fs.readFileSync('./webAppTranslationKeys.json'))

languages.forEach((languageKey) => {
  // let languageTranslations = JSON.parse(fs.readFileSync(`../webapp/public/locales/${languageKey}/translation.json`))
  let languageTranslations = {}
  keys.forEach(key => {
    const ogTranslation = translations[key]

    if(!ogTranslation) {
      console.log('🛑 Could not find translations for', key)

    languageTranslations[key] = unpackTranslation(ogTranslation, languageKey)
  fs.writeFileSync(`../webapp/public/locales/${languageKey}/translation.json`, JSON.stringify(languageTranslations, null, 2))

// Delete auto generated file

console.log('✅ Generated webapp translations')