The outputs read-only property of the MIDIAccess interface provides access to any available MIDI output ports.

A MIDIOutputMap instance.

The Navigator.requestMIDIAccess() method returns a promise that resolves with a MIDIAccess object. Printing the value of outputs to the console returns a MIDIOutputMap.

navigator.requestMIDIAccess().then((access) => {
  console.log(access.outputs);
});