I've made no attempts at all at performance tuning yet it runs very nicely in webkit browsers and not too bad in firefox.
While playing I noticed I was able to go faster than my projectile, and I was slightly disappointed when I was unable to damage my own ship that way.
You may also notice the view zooms out as your speed increases, so you have a much wider view
Bugs I noticed: All the bullets in the world sometimes disappear at once. There's no pause button.
Mostly I love the controls, except friction on your ship is a little aggressive -- I think there should be no friction if you're below a certain speed, but maybe it's just my expectations from Star Control 2 (check out the FOSS version, Ur-quan Masters, with sudo apt-get install uqm if you're on an Ubuntu-like system). Also, the game desperately needs a hold-to-fire, or even toggle fire, button. Single-shot fire in a game like this is why there was a thriving turbo controller cottage industry in the '80s - '90s.
Yes, it's a bit hard to see but I haven't really spent any time tuning it - been too busy. Did you nitice the little blue ships that you can shoot to get a token to upgrade your guns? There's red ships that follow you that show up every 30 seconds, and blue ones that contain powerups that show up after (I think) 10k points.
The code appears to be very well-structured and readable, even though it's compiled to JavaScript. IMO, a good example for those learning to use canvas (like myself). Thanks a lot for sharing.