The context is within an thread on Animation. Yes, of course it's cheap enough for an effect you are just generating a still of, but it is a measurably slow approach for anything that needs animation.

And couldn't you create the kind of library you wanted by simply making a wrapper that called did something like

    function X(canvas, ...) { var C = canvas.clone(); oldX(C, ...); return canvas }

You can't really do the opposite and get the performance advantages.