I've been looking for the same thing. I thought I saw it one time, so in my planning I didn't look again, but I guess it doesn't exist :(
The polling of current screen width to a global variable that stored the last screen size is working for me accept for when the window is maximized, then it freaks out :(
of course, it could just be that my brain has shut down for the day and I'm missing something. I'll give it another go tomorrow.
I would like to say though, that it's kind of silly that an engine that is (currently) purely html5/javascript/web-based doesn't have an "on resize" event. Maybe not enough people care? Though I'd like to know how they manage a full screen HUD (or any HUD) if the window size is smaller than the canvas? Maybe they just keep it in the 800 x 600 range and forget about it? Maybe I'm just missing something?