How to add undo-functionality to HTML5 Canvas?

On http://arthurclemens.github.io/Javascript-Undo-Manager/ I have a working example of undo with a canvas element. When you make a modification, you feed the undo manager the undo and redo methods. Tracking of the position in the undo stack is done automatically. Source code is at Github.

The other option, if you need to manipulate objects is to convert your canvas to SVG using a library that preserves the Canvas API preventing a rewrite.

At least one such library exists at this time (November 2011): SVGKit

Once you have SVG, it is much easier to remove objects and much more without the need to redraw the entire canvas.

You have to store all modifications in a datastructure. Then you can delete the latest modification if the user wants to undo it. Then you repaint all drawing operations from your datastructure again.