code: function WriteStream(opts) {
      assert.object(opts);
      if (opts.encoding !== null)
          assert.string(opts.encoding, 'options.encoding');
      assert.string(opts.flags, 'options.flags');
      assert.number(opts.mode, 'options.mode');
      assert.object(opts.fs, 'options.fs');
      assert.optionalNumber(opts.start, 'options.start');
  
      stream.Writable.call(this, opts);
  
      this.bytesWritten = 0;
      this.encoding = opts.encoding;
      this.flags = opts.flags;
      this.mode = opts.mode;
      this.start = opts.start || 0;
  
      this._fd = opts.fd;
      this._fs = opts.fs;
  
      this._opening = true;
      this._pos = this.start;
  
      var self = this;
      this.once('finish', function onFinsh() {
          if (!self._fd)
              return;
  
          self._fs.close(self._fd, function onClose(err) {
              if (err) {
                  self.emit('error', err);
              } else {
                  self.emit('close');
              }
          });
      });
  }
docs: /--- Streams