How to use the iconv-lite.getDecoder function in iconv-lite

function getDecoder (encoding) {
  if (!encoding) return null

  try {
    return iconv.getDecoder(encoding)
  } catch (e) {
    // error getting decoder
    if (!ICONV_ENCODING_MESSAGE_REGEXP.test(e.message)) throw e

    // the encoding was not found
    throw createError(415, 'specified encoding unsupported', {
      encoding: encoding,
      type: 'encoding.unsupported'
    })
  }
}

function getDecoder (encoding) {
  if (!encoding) return null

  try {
    return iconv.getDecoder(encoding)
  } catch (e) {
    // error getting decoder
    if (!ICONV_ENCODING_MESSAGE_REGEXP.test(e.message)) throw e

    // the encoding was not found
    throw createError(415, 'specified encoding unsupported', {
      encoding: encoding,
      type: 'encoding.unsupported'
    })
  }
}

function getDecoder (encoding) {
  if (!encoding) return null

  try {
    return iconv.getDecoder(encoding)
  } catch (e) {
    // error getting decoder
    if (!iconvEncodingMessageRegExp.test(e.message)) throw e

    // the encoding was not found
    throw createError(415, 'specified encoding unsupported', 'encoding.unsupported', {
      encoding: encoding
    })
  }
}

exports.decode = function(buffer, encoding, options) {
  if (Buffer.isEncoding(encoding)) {
    return buffer.toString(encoding);
  }

  const decoder = Iconv.getDecoder(encoding, options || {});

  const res = decoder.write(buffer);
  const trail = decoder.end();

  return trail ? res + trail : res;
};