function Zlib(mode) {
  if (typeof mode !== 'number' || mode < exports.DEFLATE || mode > exports.UNZIP) {
    throw new TypeError('Bad argument');
  }

  this.dictionary = null;
  this.err = 0;
  this.flush = 0;
  this.init_done = false;
  this.level = 0;
  this.memLevel = 0;
  this.mode = mode;
  this.strategy = 0;
  this.windowBits = 0;
  this.write_in_progress = false;
  this.pending_close = false;
  this.gzip_id_bytes_read = 0;
}
Emulate Node's zlib C++ layer for use by the JS layer in index.js