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

Returns a string containing the connection state of the port, one of:

"open"

The device that this MIDIPort represents has been opened and is available.

"closed"

The device that this MIDIPort represents has not been opened, or has been closed.

"pending"

The device that this MIDIPort represents has been opened but has subsequently disconnected.

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

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