browserify-cache - Strong and weak caching for Browserify bundles
"Last-Modified" and "If-Modified-Since" are "weak" caching. If the "If-Modified-Since" header is set, then Browserify can send 304 Not Modified, if appropriate, which saves bandwidth.
"Expires" or "Cache-Control: max-age" are "strong" caching. The browser can simply pull from its own cache in certain cases to save an entire HTTP request. In the client HTML, if the Browserify bundle URL contains a UNIX timestamp that matches the last modified date of the bundle. This allows a user to easily implement URL fingerprinting by simply appending the last modified date of the Browserify bundle (b.modified) to the mount URL. The full Browserify mount URL is made available via req.browserifyMount. Finally, if Express is being utilitzed, the 'browserifyMount' local is available to views via res.locals(...).
https://github.com/substack/node-browserify
http://code.google.com/speed/page-speed/docs/caching.html