Choose between javascript files for canvas randomly

Ok, for my website, I currently have the website coded like this: http://ift.tt/2m9cFov the code is too lengthy to put here. I coded another version with this background: http://ift.tt/2yLEGIY again it's to lengthy so look at the code. I would like to have it so, upon loading it randomly chooses one of the two javascript backgrounds. Does anyone know how I would do this?