How to use the whatwg-encoding.labelToName function in whatwg-encoding

const { readyState } = this;
      if (readyState === XMLHttpRequest.LOADING || readyState === XMLHttpRequest.DONE) {
        throw new DOMException("The object is in an invalid state.", "InvalidStateError");
      }

      this[xhrSymbols.flag].overrideMIMEType = "application/octet-stream";

      // Waiting for better spec: https://github.com/whatwg/xhr/issues/157
      const parsed = MIMEType.parse(mime);
      if (parsed) {
        this[xhrSymbols.flag].overrideMIMEType = parsed.essence;

        const charset = parsed.parameters.get("charset");
        if (charset) {
          this[xhrSymbols.flag].overrideCharset = whatwgEncoding.labelToName(charset);
        }
      }
    }

return whatwgEncoding.labelToName(string.substring(position + 1, nextIndex));
    }

    // It is an unmatched quotation mark
    return null;
  }

  if (string.length === position + 1) {
    return null;
  }

  let end = string.substring(position + 1).search(/\x09|\x0A|\x0C|\x0D|\x20|;/);
  if (end === -1) {
    end = string.length;
  }
  return whatwgEncoding.labelToName(string.substring(position, end));
}

function fetchStylesheetInternal(elementImpl, urlString, parsedURL) {
  let defaultEncoding = elementImpl._ownerDocument._encoding;
  if (elementImpl.localName === "link" && elementImpl.hasAttribute("charset")) {
    defaultEncoding = whatwgEncoding.labelToName(elementImpl.getAttribute("charset"));
  }

  resourceLoader.load(elementImpl, urlString, { defaultEncoding }, data => {
    // TODO: MIME type checking?
    if (elementImpl.sheet) {
      exports.removeStylesheet(elementImpl.sheet, elementImpl);
    }
    exports.createStylesheet(data, elementImpl, parsedURL);
  });
}

const { readyState } = this;
      if (readyState === XMLHttpRequest.LOADING || readyState === XMLHttpRequest.DONE) {
        throw new DOMException("The object is in an invalid state.", "InvalidStateError");
      }

      this[xhrSymbols.flag].overrideMIMEType = "application/octet-stream";

      // Waiting for better spec: https://github.com/whatwg/xhr/issues/157
      const parsed = MIMEType.parse(mime);
      if (parsed) {
        this[xhrSymbols.flag].overrideMIMEType = parsed.essence;

        const charset = parsed.parameters.get("charset");
        if (charset) {
          this[xhrSymbols.flag].overrideCharset = whatwgEncoding.labelToName(charset);
        }
      }
    }

function fetchStylesheetInternal(elementImpl, urlString, parsedURL) {
  let defaultEncoding = elementImpl._ownerDocument._encoding;
  if (elementImpl.localName === "link" && elementImpl.hasAttribute("charset")) {
    defaultEncoding = whatwgEncoding.labelToName(elementImpl.getAttribute("charset"));
  }

  resourceLoader.load(elementImpl, urlString, { defaultEncoding }, data => {
    // TODO: MIME type checking?
    if (elementImpl.sheet) {
      exports.removeStylesheet(elementImpl.sheet, elementImpl);
    }
    exports.createStylesheet(data, elementImpl, parsedURL);
  });
}

function fetchStylesheetInternal(elementImpl, urlString, parsedURL) {
  const document = elementImpl._ownerDocument;
  let defaultEncoding = document._encoding;
  const resourceLoader = document._resourceLoader;

  if (elementImpl.localName === "link" && elementImpl.hasAttributeNS(null, "charset")) {
    defaultEncoding = whatwgEncoding.labelToName(elementImpl.getAttributeNS(null, "charset"));
  }

  function onStylesheetLoad(data) {
    const css = whatwgEncoding.decode(data, defaultEncoding);

    // TODO: MIME type checking?
    if (elementImpl.sheet) {
      exports.removeStylesheet(elementImpl.sheet, elementImpl);
    }
    exports.createStylesheet(css, elementImpl, parsedURL);
  }

  resourceLoader.fetch(urlString, {
    element: elementImpl,
    onLoad: onStylesheetLoad
  });

readAsText(file, encoding) {
    this._readFile(file, "text", whatwgEncoding.labelToName(encoding) || "UTF-8");
  }

function finalCharset(xhr) {
  const flag = xhr[xhrSymbols.flag];
  if (flag.overrideCharset) {
    return flag.overrideCharset;
  }
  const parsedContentType = MIMEType.parse(getResponseHeader(xhr, "content-type"));
  if (parsedContentType) {
    return whatwgEncoding.labelToName(parsedContentType.parameters.get("charset"));
  }
  return null;
}

function finalCharset(xhr) {
  const flag = xhr[xhrSymbols.flag];
  if (flag.overrideCharset) {
    return flag.overrideCharset;
  }
  const parsedContentType = MIMEType.parse(getResponseHeader(xhr, "content-type"));
  if (parsedContentType) {
    return whatwgEncoding.labelToName(parsedContentType.parameters.get("charset"));
  }
  return null;
}

function finalCharset(xhr) {
  const flag = xhr[xhrSymbols.flag];
  if (flag.overrideCharset) {
    return flag.overrideCharset;
  }
  const parsedContentType = MIMEType.parse(getResponseHeader(xhr, "content-type"));
  if (parsedContentType) {
    return whatwgEncoding.labelToName(parsedContentType.parameters.get("charset"));
  }
  return null;
}