Forget it, can't find it anymore I was under the impression that Slug was the Webclient version of Slack, but I guess they just reimplement the adress stripping there.
the Stuff is written mainly by Jed Watson, do a search in the source bundle.js and find:
/*!
Copyright (c) 2015 Jed Watson.
Based on code that is Copyright 2013-2015, Facebook, Inc.
All rights reserved.
*/
---------------------------
Basically it is against all odds that they were able to pull out a chat client that connects 1000s of users without a problem on day one ... something that discord and slack took years - there has to be one of the base engines in the background - but except the visible JS code I have no proof anymore :(
The Facebook stuff seems to be more than just the emojis and there is alot MIT license stuff in there (which would be fine) (facebook stuff maybe not so fine)