You can achieve this by different methods like:
- long polling: long polling is kinda event driven notifying where sever responds back when there is a change (holds the request until data is available)
- Short polling - Periodically (for eg, every 30 seconds) hitting the server with ajax request to get fresh data
Both the above techniques are old and not recommended now as you have latest features like HTML5 WebSockets and WebRTC in modern browsers. What you need here is a push from server side whenever there is a change.
I would recommened you to have a look into SignalR (http://www.asp.net/signalr) if you are using dotnet backend or if its node backend, then node implementation of signalr (npmjs.com/package/signalrjs).
ASP.NET SignalR is a new library for ASP.NET developers that makes
developing real-time web functionality easy. SignalR allows
bi-directional communication between server and client. Servers can
now push content to connected clients instantly as it becomes
available. SignalR supports Web Sockets, and falls back to other
compatible techniques for older browsers. SignalR includes APIs for
connection management (for instance, connect and disconnect events),
grouping connections, and authorization.
Update - Just saw an awesome detailed explanation in SO which would give you more insight (may be the question is different, but the answer given is something which would help you) - In what situations would AJAX long/short polling be preferred over HTML5 WebSockets?