The state read-only property of the MIDIPort interface returns the state of the port.

A string containing the state of the port, one of:

"disconnected"

The device that this MIDIPort represents is disconnected from the system.

"connected"

The device that this MIDIPort represents is currently connected.

The following example loops through all input ports and prints the state of each to the console.

for (const entry of midiAccess.inputs) {
  const input = entry[1];
  console.log(input.state);
}