How to listen if a device connected or not

[youesei]

Hello, I am doing a project that reads the pulses of an ecoder through an Arduino 1 with Nodejs, how can I make my code listen if there is a device on a port, if there is not or if it has just been connected, but not executing a block of code from time to time checking if there is a device or not as a setInterval does, if not it is always listened to (as sockets do). Thanks in advance for the help