[ris]

Great - use the hash of an obscure site specific script, then detect how quickly the script loads and you know whether your victim has visited the site because they have it in their cache. Looks like a surefire route to a cache information leak to me.

[cbr]

You can already do that.

     good.com:
        <script src="/js/site.js">

     evil.com:
        <img src="https://www.good.com/js/site.js">

Then use the navigation timing api to figure out whether the js was already in cache.

[cbr]

(Actually, you could use the onload event; you don't actually need navigation timings.)

[opendais]

Cache information leakage for common js libraries is a non-issue compared to a CDN being compromised and mass MITMing via javascript libraries.

Even things like NoScript don't stop that vector if you whitelist common CDN's like google's.

[realusername]

The main goal of a technology like this is to help the caching of common scripts, not to cache your entire website.

The only information you could have with this is that the browser already downloaded jquery from another website, that is not going to help that much.