source.onmessage is the built in function wrapper for EventSource that is triggered when new data is sent to the client. It fires when no event attribute is returned (default) and doesn’t fire when it is set. addEventListener is similar, but differs in that it listens for a specific event name, and triggers on its presence, … Read more
SSE is a text-based protocol, and curl is a great way to troubleshoot exactly what your connection is sending. The command is this simple: curl -N http://127.0.0.1/path/to/clock.php (The -N stops any buffering, so data is shown as it is received.) And it outputs this: data:2015-07-07 06:19:27 data:2015-07-07 06:19:28 data:2015-07-07 06:19:29 data:2015-07-07 06:19:30 data:2015-07-07 06:19:31 data:2015-07-07 … Read more
The Push API allows the server to send a notification to a client even when your site is not open, because it relies on service workers. SSE (or WebSockets) work as long as the user is using your site. There are some examples (with documentation) in the Web Push section of the ServiceWorker Cookbook that … Read more
The way this works in all browsers are that each domain gets a limited amount of connections and the limits are global for your whole application. That means if you have one connection open for realtime communication you have one less for loading images, CSS and other pages. On top of that you don’t get … Read more
In a word, no. Microsoft has not included SSE or an equivalent of SSE in any version of IE. IMO, you have two good options: Use a polyfill – My tests with this polyfill in IE10 and IE11 were all successful. Since it starts with if (“EventSource” in global) return;, it’ll only run in browsers … Read more
No, the SSE standard does not allow POST. (For no technical reason, as far as I’ve been able to tell – I think it was just that the designers never saw the use cases: it is not just large data, but if you want to do a custom authentication scheme there are security reasons not … Read more
Server Side Events work differently in all of the browsers, but they all close the connection during certain circumstances. Chrome, for example, closes the connection on 502 errors while a server is restarted. So, it is best to use a keep-alive as others suggest or reconnect on every error. Keep-alive only reconnects at a specified … Read more
The HTML5 doctor site has a great write-up on server-sent events, but I’ll try to provide a (reasonably) short summary here as well. Server-sent events are, at its core, a long running http connection, a special mime type (text/event-stream) and a user agent that provides the EventSource API. Together, these make the foundation of a … Read more
Is there a name for Google’s solution for real-time updates in Drive (such as “long polling” or “sockets”)? It didn’t have a name until now. I’ll call it “no-polling,” to contrast with polling and long-polling. With polling, the client periodically sends queries for new data. With long-polling, the client queries for data, and the server … Read more
Ajax polling adds a lot of HTTP overhead since it is constantly establishing and tearing down HTTP connections. As HTML5 Rocks puts it “Server-Sent Events on the other hand, have been designed from the ground up to be efficient.” Server-sent events open a single long-lived HTTP connection. The server then unidirectionally sends data when it … Read more