The server doesn't [have to] return the entire page on a change. Return small chunk of HTML or small chunk of JSON. There will be a small cost to do the HTML on

The server doesn't [have to] return the entire page on a change. Return small chunk of HTML or small chunk of JSON. There will be a small cost to do the HTML on the server but there is also a cost to do the HTML on the client: sending them 50000000000kb of JavaScript initially.