So, I'm poking around at ways to bulge my brain into this Centro and hacking a bit. I see that the built-in browser, Blazer, claims to support JavaScript. I've yet to see any evidence of this, though I do indeed have a "Disable JavaScript" checkbox in preferences which is duly unchecked.
I don't really care about Blazer supporting JS in the sense that it works with existing sites - I'd just like to make something for myself involving JS that works on my Centro. But it seems like a big no-op.