close(code, data, mask, cb) {
    let buf;

    if (code === undefined) {
      buf = EMPTY_BUFFER;
    } else if (typeof code !== 'number' || !isValidStatusCode(code)) {
      throw new TypeError('First argument must be a valid error code number');
    } else if (data === undefined || !data.length) {
      buf = Buffer.allocUnsafe(2);
      buf.writeUInt16BE(code, 0);
    } else {
      const length = Buffer.byteLength(data);

      if (length > 123) {
        throw new RangeError('The message must not be greater than 123 bytes');
      }

      buf = Buffer.allocUnsafe(2 + length);
      buf.writeUInt16BE(code, 0);

      if (typeof data === 'string') {
        buf.write(data, 2);
      } else {
        buf.set(data, 2);
      }
    }

    const options = {
      [kByteLength]: buf.length,
      fin: true,
      generateMask: this._generateMask,
      mask,
      maskBuffer: this._maskBuffer,
      opcode: 0x08,
      readOnly: false,
      rsv1: false
    };

    if (this._state !== DEFAULT) {
      this.enqueue([this.dispatch, buf, false, options, cb]);
    } else {
      this.sendFrame(Sender.frame(buf, options), cb);
    }
  }
Sends a close message to the other peer.

@param {Number} [code] The status code component of the body
@param {(String|Buffer)} [data] The message component of the body
@param {Boolean} [mask=false] Specifies whether or not to mask the message
@param {Function} [cb] Callback
@public