socket.io is probably one of the most unnecessary libraries on this planet. Websockets are already as simple as possible.
In fact, websockets work so well I use them as a generic TCP replacement, because the message oriented transport model gives me 99% of what I need with the exception of custom message types. Leaving that out was a massive letdown to me, because you now need to carry a way to identify the message type inside the body, rather than just throwing the message itself into the appropriate protocol parser (e.g. a schema based binary format).
In fact, websockets work so well I use them as a generic TCP replacement, because the message oriented transport model gives me 99% of what I need with the exception of custom message types. Leaving that out was a massive letdown to me, because you now need to carry a way to identify the message type inside the body, rather than just throwing the message itself into the appropriate protocol parser (e.g. a schema based binary format).