Server-Sent Events allow a web page to get updates from a server.
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.
Server-Sent Events are supported in all major browsers, except Internet Explorer.
The EventSource object is used to receive server-sent event notifications:
In the tryit example above there were some extra lines of code to check browser support for server-sent events:
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):
Code in ASP (VB) (demo_sse.asp):
In the examples above we used the onmessage event to get messages. But other events are also available:
|onopen||When a connection to the server is opened|
|onmessage||When a message is received|
|onerror||When an error occurs|