How could I get access to socket.io.min.js in express?

Socket.IO intercepts requests to /socket.io to serve the files it needs. It normally serves them from:

./node_modules/socket.io/node_modules/socket.io-client/dist

However, as said in Socket.IO's wiki, you can serve the files yourself if you prefer.

The files you need are in the /dist folder in the socket.io-client repo.

If you want to force production settings all the time, you can just add this to your node app right before calling listen():

io.enable('browser client minification');  // send minified client
io.enable('browser client etag');          // apply etag caching logic based on version number
io.enable('browser client gzip');          // gzip the file
io.set('log level', 1);                    // reduce logging
io.set('transports', [                     // enable all transports (optional if you want flashsocket)
    'websocket'
  , 'flashsocket'
  , 'htmlfile'
  , 'xhr-polling'
  , 'jsonp-polling'
]);

Latest socket.io.js minified version here, as of today (version 0.9.16):

http://cdnjs.cloudflare.com/ajax/libs/socket.io/0.9.16/socket.io.min.js