Are you crying out for something more interesting than boilerplate setup code? Here’s the good news: From here on it gets much more interesting. Start by adding an animated starfield onto the page to give the game some space-like qualities.
You can create a scrolling starfield in a few ways, but in this case you need to be a little careful with the number of objects that get drawn on the screen because drawing too many sprites per frame slows down the game on mobile devices. One way around this is to create an offscreen canvas buffer, draw a bunch of random stars on that buffer, and then simply draw that starfield moving slowly down the canvas. You’ll be limited to a few different layers of moving stars, but this effect should be good enough for a retro shooter.