safe-react/config/polyfills.js

// @flow
if (typeof Promise === 'undefined') {
  // Rejection tracking prevents a common issue where React gets into an
  // inconsistent state due to an error, but it gets swallowed by a Promise,
  // and the user has no idea what causes React's erratic future behavior.
  require('promise/lib/rejection-tracking').enable()
  window.Promise = require('promise/lib/es6-extensions.js')
}

// fetch() polyfill for making API calls.
require('whatwg-fetch')

// Object.assign() is commonly used with React.
// It will use the native implementation if it's present and isn't buggy.
Object.assign = require('object-assign')