Tutorials References Exercises Bootcamp Menu
Sign Up Create Website Get Certified Upgrade

HTML Tutorial

HTML HOME HTML Introduction HTML Editors HTML Basic HTML Elements HTML Attributes HTML Headings HTML Paragraphs HTML Styles HTML Formatting HTML Quotations HTML Comments HTML Colors HTML CSS HTML Links HTML Images HTML Favicon HTML Page Title HTML Tables HTML Lists HTML Block & Inline HTML Classes HTML Id HTML Iframes HTML JavaScript HTML File Paths HTML Head HTML Layout HTML Responsive HTML Computercode HTML Semantics HTML Style Guide HTML Entities HTML Symbols HTML Emojis HTML Charset HTML URL Encode HTML vs. XHTML

HTML Forms

HTML Forms HTML Form Attributes HTML Form Elements HTML Input Types HTML Input Attributes HTML Input Form Attributes

HTML Graphics


HTML Media

HTML Media HTML Video HTML Audio HTML Plug-ins HTML YouTube


HTML Geolocation HTML Drag/Drop HTML Web Storage HTML Web Workers HTML SSE

HTML Examples

HTML Examples HTML Editor HTML Quiz HTML Exercises HTML Certificate HTML Summary HTML Accessibility

HTML References

HTML Tag List HTML Attributes HTML Global Attributes HTML Browser Support HTML Events HTML Colors HTML Canvas HTML Audio/Video HTML Doctypes HTML Character Sets HTML URL Encode HTML Lang Codes HTTP Messages HTTP Methods PX to EM Converter Keyboard Shortcuts


Server-Sent Events (SSE) allow a web page to get updates from a server.

Server-Sent Events - One Way Messaging

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.

Browser Support

The numbers in the table specify the first browser version that fully support server-sent events.

SSE 6.0 79.0 6.0 5.0 11.5

Receive Server-Sent Event Notifications

The EventSource object is used to receive server-sent event notifications:


var source = new EventSource("demo_sse.php");
source.onmessage = function(event) {
  document.getElementById("result").innerHTML += event.data + "<br>";
Try it Yourself »

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"

Check Server-Sent Events Support

In the tryit example above there were some extra lines of code to check browser support for server-sent events:

if(typeof(EventSource) !== "undefined") {
  // Yes! Server-sent events support!
  // Some code.....
} else {
  // Sorry! No server-sent events support..

Server-Side Code Example

For the example above 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". Now you can start sending event streams.

Code in PHP (demo_sse.php):

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

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

Code in ASP (VB) (demo_sse.asp):

Response.ContentType = "text/event-stream"
Response.Expires = -1
Response.Write("data: The server time is: " & now())

Code explained:

  • Set the "Content-Type" header to "text/event-stream"
  • Specify that the page should not cache
  • Output the data to send (Always start with "data: ")
  • Flush the output data back to the web page

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