Cross-Platform and / or HTML 5 Multiplayer

I could write my own networking using HTTP, but I’d like to avoid having to do that and use as much out-of-the-box stuff as possible. Socket based networking would be nice, but I’m not sure how an HTML application would work in this regard - am I still reduced to writing my own networking code?

I’m not sure what has to do with any of this, could you elaborate?