Can you also make use of other non-GPL libraries on your website then? I would assume this would realistically only affect the portion of your code that interacts with Tremula
> I would assume this would realistically only affect the portion of your code that interacts with Tremula
Yes if those portions are separate pages, otherwise no. The GPL doesn't permit linking to (i.e. calling into or calling from) non-GPL'd code . The GPL FAQ states that an exception to the GPL is needed in order to permit JavaScript library calls, see http://www.gnu.org/licenses/gpl-faq.html#WMS. Any application code which interacts with Tremula must be under the GPL and any libraries it uses must be GPL compatible. Any code which calls into that application code will also need to be under the GPL too.
