Today I was filling one online form with 100 plus checkboxes, after checking 4-5 boxes, felt bored. So, wrote a simple javascript function and ran it through firefox's firebug console and checked all boxes with just one click on run.
I had a simple one with no if conditions, but decided to make it better so i could use it on my websites. So here you go, a very simple JS check and uncheck all checkboxes functions. Just one function handles both options.