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.
Receive Server-Sent Event Notifications
var source = new EventSource("demo_sse.php");
source.onmessage = function(event) {
document.getElementById("result").innerHTML += event.data + "<br>";
};
//Example explained:
// - Create a new EventSource object, and specify the URL of the page sending
//the updates (in this example "demo_sse.php")
// - Each time an update is received, the onmessage event occurs
// - When an onmessage event occurs, put the received data into the element
//with id="result"
The EventSource object is used to receive server-sent event notifications.
Check Server-Sent Events Support
Server-Side Code Example
//Code in PHP (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();
?>
//Code in ASP (VB) (demo_sse.asp)
<%
Response.ContentType = "text/event-stream"
Response.Expires = -1
Response.Write("data: The server time is: " & now())
Response.Flush()
%>
For the example to work, you need a server capable of sending data updates (like PHP or ASP).
The server-side event stream syntax is simple. Set the "Content-Type" header to "text/event-stream".