onevent(packet) {
        const args = packet.data || [];
        if (null != packet.id) {
            args.push(this.ack(packet.id));
        }
        if (this.connected) {
            this.emitEvent(args);
        }
        else {
            this.receiveBuffer.push(Object.freeze(args));
        }
    }
Called upon a server event.

@param packet
@private