How can i get latest or fresh data from server (if in server happened new event (for example there are 2 users x,y and x send messages to y and y get this message without refreshing page ) )? I don't want to use setInterval because it repeats all message again and again. Is there any Technique that can i use for this ? I heard about Ajax that technique need to send request to the server but i want when happen an event in the server and webpage get it without refreshing..
The first technique is the long polling, which sends request to the server and waits until the server sends something, for example the new message. You must re-send requests to the server each time you get a new message or your request is time out. This technique uses AJAX. Long polling PHP example - How do I implement basic "Long Polling"?
The second is web sockets, https://en.wikipedia.org/wiki/WebSocket
this stackoverflow question deals with the implementation of websocket.
socket.io has a demo of chat application.
If you looking for bidirectional full duplex method then go for WebSockets but for just polling data from server you can use Server Sent Event as well. Adding reference links for both:
WebSocket:
http://html5demos.com/web-socket
http://en.wikipedia.org/wiki/WebSocket
HTML5 Websockets for Realtime Chat app?
SSE:
http://www.html5rocks.com/en/tutorials/eventsource/basics/
Examples: