A shorter version of the word "Just".
This can often be used to increase typing speeds or can be used by "gangsters" who think they are worth more than shit.
This shortened version can be often times useful if you are playing a fighting game and are trying to get a message across all whilst fighting someone. Me personally, I don't really care for typing speeds, as I already have a good one of 80 WPM.
"Js leave me alone man!"
"You are js so annoying."
On Emtek's stream it means "Jebać Soapa" (eng. Fck the Soap)
Soap: Please remove that link from the channel.
Person: JS
Soap: User "Person" has been banned.
BIG DICKKK BROOOO OUUU YEETT, he kisses good, fucks good, and is all the girls want