ReferenceError: regeneratorRuntime is not defined (but working inside a scope)

I know this has been answered but, unfortunately, they didn't fix the problem for me. what solved it was to import babel babel-polyfills inside the file

import "core-js/stable";
import "regenerator-runtime/runtime";

you can find it on the official babeljs documetation orat this article

Also you could do the following with es2015 preset and transform-regenerator plugin:

.babelrc

{
  "presets": ["es2015"],
  'plugins': [
    'transform-regenerator'
  ]
}

Code

let regeneratorRuntime =  require("regenerator-runtime");
// You code with ES6 generators

P.S. Of course you should install babel-plugin-transform-regenerator npm package.

Babel assumes that the polyfill will be loaded before anything else in your application, but you're using a function declaration, which is hoisted, meaning that it exists and is usable before require has been called.

In the case of generators, then need regeneratorRuntime which is provided by the polyfill, but the polyfill hasn't loaded when the regenerator is initialized.

The Babel team's recommendation is to make two files:

index.js

require('babel-polyfill');
require('./app');