[React Intl] Use Webpack to Conditionally Include an Intl Polyfill for Older Browsers

if (!window.Intl) {
  require.ensure([
    'intl',
    'intl/locale-data/jsonp/en.js',
    'intl/locale-data/jsonp/fr.js',
    'intl/locale-data/jsonp/es.js'
  ], (require) => {
    require('intl');
    require('intl/locale-data/jsonp/en.js');
    require('intl/locale-data/jsonp/fr.js');
    require('intl/locale-data/jsonp/es.js');

    runApp();
  })
} else {
  runApp();
}

function runApp() {
  addLocaleData([...en, ...fr, ...es]);

  let locale = (navigator.languages && navigator.languages[0])
    || navigator.language
    || navigator.userLanguage
    || 'en-US';

  ReactDOM.render(
    <IntlProvider locale={locale} messages={flattenMessages(messages[locale])}>
      <App />
    </IntlProvider>,
    document.getElementById('root')
  );
}