iepolyfill.js

export function getIePolyfill(siteDir: string) {
  let iePolyfill = '';
  const env =
    process.env.NODE_ENV === 'production' ? 'production' : 'development';
  const supportedBrowsers = browserslist(undefined, {path: siteDir, env});

  if (
    supportedBrowsers.includes('ie 9') ||
    supportedBrowsers.includes('ie 10')
  ) {
    iePolyfill = 'react-app-polyfill/ie9';
  } else if (supportedBrowsers.includes('ie 11')) {
    iePolyfill = 'react-app-polyfill/ie11';
  }
  return iePolyfill;
}