With the dynamic properties of JavaScript, it's often difficult to distinguish between library code and original code that is relevant to the website. Modifications can be made in separate files, but they could be directly or indirectly modifying library code. As far as I can tell this means that, if I were to use a GPLed JavaScript library when building a web-site, the licensing for the rest of the site becomes murky.
Given these assumptions (please correct me if I am wrong), when, and how, does it make sense to use GPLed JavaScript libraries?