Is there a way to allow a user, after he has created a vector graph on a javascript svg canvas using a browser, to download this file to their local filesystem?
SVG
No need to do any programming at all. There are online apps people have already built for that, and include definable parameters such as dimensions, resolution, output format etc.
This is one of the better online image conversion apps I've found for svg->jpeg.http://image.online-convert.com/convert-to-jpg