In notebook:
FrontEndMasters Real-Time Web with Node.js
Created at:
JavaScript Fundamentals libraries
Video Course on Real-Time HTML5 with Node.jsnobody does WebSockets directly without a facade, but use frameworks e.g. socket.io or pusherajax is a roundtrip 

there's an overhead for client initiating a request, the server a response and http packerts have extra 200 or more bytes 

ajax is only when you need updates every 5 minutes, but not when 5 request per second (e.g. games)
in average an ajax request is about 500 - 800ms roundtrip 

in websocket, there's an inital socket opening, then in either direction the header is 8 bytes, we don't pay the penalty to open and close connection

the latency is 50 - 100 ms 

but even 100ms can be too slow in fact
"real-time" is a misnomer : it's sub microsecond or nanosecond 

we mean "near real-time"  
it's more resource intensive for the server: you need so many ports open
but in general it uses less bandwidth
the pattern is same for client or server. in general

socket.on("eventname" function(data){  
  self.postMessage({error: "game_session_invalid"});


socket.emit("another_event_name", {game_session_id: bar});

client and server can listen to send events (​emit​) and send data (JS objects) along 

in addition the server can broadcast​ a message to all clients (it doesn't exist on the client)