I think for me it depends on the situation. If it is on a facebook private chat or group chat, I type how I speak. I regularly say and type "hell yeah" and we have this thing where if anyone in the group compliments to does something for another, we reply with "Thank" and the other will say "Welc" instead of thank you and you're welcome. I also do it to an extent here as I'm quite chilled and stuff so I don't try too hard to seem quite professional and stuff, but at the same time, i'm normally quite proper anyway except for the 'friend memes' and jokes that I'll refer to and stuff so even in my 'professional' typing I somewhat type how I usually would anyway, I just tend to use a few more long professional words instead of stuff like "OMG WTF That's so gr9, Thank." or something that I would send to friends. haha.