[pluma]

In theory public CDNs are the solution. In practice it only works if a critical mass of websites use them.

As others have pointed out, the version matters. There are a gazillion different versions of jQuery out there and many websites are very slow to update them if ever. So you only benefit by visiting multiple sites that use exactly the same version.

Additionally there is a ton of different public CDNs. Now, jQuery itself has solved this by providing an official jQuery CDN and pushing it to developers. In fact, the first result for "jQuery CDN" is their own website.

I'd say jQuery is probably the least bad example of this. If you visit enough websites there's a non-zero chance you'll have a CDN cache hit for jQuery on a few of them.

The problem is that jQuery rarely comes alone. Even jQuery UI is less widely deployed than jQuery and thus less likely to be cached from a CDN. But once you get into plugin territory or third-party libraries all bets are off.

I'm fairly certain that jQuery is the only library that has some realistic chance of benefiting from a public CDN. Everything else is probably asking for trouble (if only because you're adding unnecessary single points of failure).