Is there a way to automatic find plex servers in Network with javascript/jQuery?
Hm. There is the bonjour interface as well as PlexGDM. Unfortunately I don't know about an implementation in .js/jQuery. I guess, there are some, though.
I have some bonjour code in C. And there is PlexGDM in C# (https://github.com/quiqueck/Plex-ATV-Plugin) or Python (hippojay) (https://github.com/hippojay/plugin.video.plexbmc). You could have a look and translate them, if nothing else helps.
I am sure, there are others... but maybe this is a start for your search.
Yeah, it's pretty easy to do:
1. Send a UDP message to the multicast address 239.0.0.250 on port 32414: M-SEARCH * HTTP/1.0
2. listen for responses from each PMS returned to port 32414 starting "200 OK"
The returned message body will contain some information about the server - the source IP of this message will be the PMS IP.
As Baa linked to - a python implementation is here: https://github.com/hippojay/plugin.video.plexbmc/blob/frodo/resources/lib/plexgdm.py