Server polling with JavaScript

You may want to use jQuery's Ajax functions to poll the server every second or so. Then the server can respond with instructions to the browser in near real-time.

You can also consider long polling instead of the above, to reduce the latency without increasing the frequency of the polls.

Quoting Comet Daily: The Long-Polling Technique:

The long-polling Comet technique is a technique that optimizes traditional polling to reduce latency.

Traditional polling sends an XMLHttpRequest to the server in fixed intervals. For example, open a new XMLHttpRequest every 15 seconds, receive an immediate response, and close the connection.

Long-polling sends a request to the server, but a response is not returned to the client until one is available. As soon as the connection is closed, either due to a response being received by the client or if a request times out, a new connection is initiated. The result is a significant reduction in latency because the server usually has a connection established when it is ready to return information to return to the client.

In addition to the above, I also suggest that you check out the accepted answer to the following Stack Overflow post for a detailed description of the long polling technique:

• How does facebook, gmail send the real time notification?

As of 2018 you should use the fetch function with promise syntax:

<script type="text/javascript">
setInterval(function(){
  fetch("your_serverside_script.php") // Any output from the script will go to the "result" div
  .then(response => response.text())
  .catch(error => document.getElementById("result").innerHTML = error)
  .then(response => document.getElementById("result").innerHTML = response)
}, 1000); // Poll every 1000ms
</script>

<div id="result">result will appear here</div>

I second Daniel's suggestion to use long-poll or push. Check out

• CometD Bayeux Ajax Push

CometD is a scalable HTTP-based event routing bus that uses a Ajax Push technology pattern known as Comet. The term 'Comet' was coined by Alex Russell in his post Comet: Low Latency Data for the Browser.

They have a page explaining how to get that work with Spring:

• http://cometd.org/documentation/cometd-java/server/services/integration-spring