Can you combine GPL and Proprietary Javascript code ?

I am not a lawyer and this article does not represent a legal advise.

Javascript GPL code with non-free code

Basically from my research I understood that GPL Javascript will "infect" other code it is being bundled with. However it would not "infect" the html templates according to answer in the F.A.Q. at http://www.gnu.org/licenses/old-licenses/gpl-2.0-faq.html#WMS. Again I am not a lawyer and you should contact the FSF or an appropriate lawyer for your own scenario.

My recommendation as a developer

I recommend not releasing Javascript code under GPL or LGPL. There are better suited license for Javascript that can allow your code to be open-source while being friendly with other Javascript bundles.

But WordPress is GPL v2 !

Yes, that means if you release a WordPress plugin or theme with some cool Javascript code, then you should expect that Javascript code to fall under open-source GPL.

More bedtime reading

http://www.gnu.org/philosophy/javascript-trap.html