Traditionally, a web page has to send a request to the server to receive new data; that is, the page requests data from the server. With server-sent events, it's possible for a server to send new data to a web page at any time, by pushing messages to the web page. These incoming messages can be treated as Events + data inside the web page.

To learn how to use server-sent events, see our article Using server-sent events.

EventSource

Defines all the features that handle connecting to a server, receiving events/data, errors, closing a connection, etc.

• Simple SSE demo using PHP

• Mercure: a real-time communication protocol (publish-subscribe) built on top of SSE
• EventSource polyfill for Node.js
• Remy Sharp's EventSource polyfill
• Yaffle's EventSource polyfill
• Rick Waldron's jquery plugin
• intercooler.js declarative SSE support

• AJAX
• JavaScript
• WebSockets

• A Twitter like application powered by server-sent events and its code on GitHub.
• HTML5 and Server-sent events