A simple way to get there is to store each function and arguments in an object, as a list of draw operations, instead of executing the functions. Add in an object id (list index) to return to the caller, and then the caller can modify parsmter values between frames.

Do you know of any resources or examples that demonstrate basic animation techniques like this? The canvas examples I've found so far seem to be for fluid animations or games, rather than interactive scenes or visualisations that can be stopped or stepped through.