Gets all Response Headers for the current document

get-headers.ts

/**
 * Gets all Reponse Headers for the current document.
 * @returns An object cointaining the key-value pairs for each header
 */
function getHeaders(url = document.location.href) {
  const req = new XMLHttpRequest();
  req.open("GET", url, false);
  req.send(null);

  let key: string;
  let value: string;
  let colon: number;

  const headers = req.getAllResponseHeaders().split(/\n/).filter(Boolean);
  const data = headers.reduce((pairs, header) => {
    // some values contains ":" then, the split method is not recommended
    colon = header.indexOf(":");
    key = header.substring(0, colon);
    value = header.substring(colon + 1);
    pairs[key] = value;
    return pairs;
  }, new Object());

  data["Referer"] = document.referrer;
  data["UserAgent"] = navigator.userAgent;

  return data;
}