Suspicious javascript opening a web socket on localhost

[marchold]

I was looking at some code on our site today when I noticed a suspicious error in the JavaScript console.  The code was trying to open a websocket on localhost. Does anyone know where this sort of code would be coming from. 

 

[Benjaminka]

This seems to be connected to the Facebook Pixel and is probably an error on their side. Here you can find a thread about more people complaining about the same error: https://developers.facebook.com/community/threads/317050484803752/ , regarding the question why they use a websocket there is no clear answer, but it's probably used for Realtime Analytics