Uint8Array - is it really an array? And what about the other Uint#Arrays?

I guess I could add a read function that would pump out however many bytes were needed - as you say, 0xFF might be best. It's not a massive problem to create an array of bytes to stick into send though.

You could always write something like:

if (!SPI.prototype.read) SPI.prototype.read = function(n,p) { var a = new Uint8Array(n); a.fill(0xFF); return this.send(a,p); }

and then if a read function does get added, you code should swap over gracefully.

In terms of expecting data - I think you just have to 'know' - sometimes you can ask the device, but sometimes you'll just have to check the datasheet and figure it out.