What are some good practices for polling a server with JavaScript for an application that needs to refresh data very rapidly? I'm using jQuery for front-end and Java Spring Framework for backend.
Example of refreshed data could be list of items that are getting updated very rapidly (every 1 second).
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
XMLHttpRequestto the server in fixed intervals. For example, open a newXMLHttpRequestevery 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:
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 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:
