(function () {
  var date = new Date(2016, 0, 1); // January, 1st 2016
  var locale = "en-us"; // Other locales won't work as well, btw.
  var format = { month: "long" }; // Valid date format according to the Intl spec.
  // Use the IntlPolyfill version of Date.toLocaleString even if the environment won't
  // actually need the polyfill 
  var str = IntlPolyfill.__localeSensitiveProtos.Date.toLocaleString.bind(date)(locale, format);
  if (str !== "January") {
    throw new Error("Intl polyfill is still defunct. Expected: 'January', got: '" +  str + "'!");
  }
})();