Server-sent events are a perfect tool if you want to receive a series of messages from the web server. But the communication is completely one-sided. There’s no way for the browser to respond, or to enter into a more complex dialogue.

If you’re creating a web application where the browser and the web server need to have a serious conversation, your best bet (without adopting Flash) is to use the XMLHttpRequest object. Depending on the sort of application you’re building, this approach may work fine. However, there are stumbling blocks aplenty. First, the XMLHttpRequest object doesn’t work well if you need to send multiple messages back and forth very quickly (like you might in a chat application, for example). Second, there’s no way to associate one call with the next, so every time the web page makes a request, the web server needs to sort out who you are all over again. If your web page needs to m....