I would like to find or create a function that creates a Virtual MIDI device from Chrome.
This way I would find this Virtual MIDI Device/Port in my favorite DAW or else.
Is it possible in javascript or do I need to develop a plugin for that?
No, this isn't possible directly. You would need to develop a native application that could be called from a Chrome extension which could be called from the page. Also, virtual MIDI loopback drivers are different on every platform.