ReferenceError: Can't find variable: Promise. This seemed like a strange error and ultimately it turns out that
Intl.js, the ECMAScript (ECMA-402) Internationalization API.
Polyfills make sense if you're going to be using a limited sub-set of ES6 features and are okay adding a dependencies. If you plan on using the ES6 whole kit and caboodle, you're better off setting up
All you need to do is install the package and you can go about using Promises in whatever context you like.
npm install promise-polyfill
Not every polyfill will be this simple and it goes without saying that you should read the docs before installing any polyfills.