It just spins up a background process when a canvas context is created and
sends drawing commands through IPC. As a result, you can rm the 970k canvas
binary (most of it is just Unifont) and with some luck you will only break
canvas rendering.
Of course this only works for things that are relatively self-contained. So
you can add/remove image decoders or protocol handlers without recompiling
(the main binary has zero networking code), but the JS API is still baked
in.
(I imagine you could also implement some less performance-sensitive APIs in
JS and load the bytecode on demand, but I haven't tried.)
