What is mean by sse ?

SSE - server sent events

A server-sent event is when a web page automatically gets updates from a server.

This was also possible before, but the web page would have to ask if any updates were available. With server-sent events, the updates come automatically.

Examples: Facebook/Twitter updates, stock price updates, news feeds, sport results, etc.

demo_sse.php

<?php
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');

$time = date('r');
echo "data: The server time is: {$time}\n\n";
flush();
?>

<script>

if(typeof(EventSource) !== "undefined") {

    var source = new EventSource("demo_sse.php");

    source.onmessage = function(event) {

        document.getElementById("result").innerHTML += event.data + "<br>";

    };

} else {

    document.getElementById("result").innerHTML = "Sorry, your browser does not support server-sent events...";

}

</script>

The EventSource Object

In the examples above we used the onmessage event to get messages. But other events are also available:

Events	Description
onopen	When a connection to the server is opened
onmessage	When a message is received
onerror	When an error occurs