Websocket与AJAX相比，对于使用PHP的简单应用程序的优势

Question

I've used a bit of AJAX with PHP for things like submitting forms and I've recently started looking into websockets. I followed this tutorial to understand the basics. From what I gather, websockets keep the connection open whereas AJAX opens and closes a request.

My question is do websockets provide any advantage over AJAX if you're just submitting forms or simple tasks like auto_complete (which there's a jQuery plugin for anyway)? Maybe the tutorial isn't the greatest, but it seems like there's a heck of a lot more code involved to get websockets to work(at least with PHP) than just a simple AJAX call (or using jQuery which bundles it). I've read in a few places that it's a bit quicker, but if I'm working on something that isn't receiving tons of requests, will it really make a difference? Correct me if I'm wrong, but not all browsers support websockets either, right?

Answer 1

Websockets have two advantages.

1. they have much less overhead, which results in a better network performance

2. they allow the server to send data which the client hasn't explicitely requested.

The second one is the most important advantage.

In AJAX, everything the server sends must be the response to a previous request by the client, and every request can only be answered once. But in many applications, especially multi-user applications, events happen on the server and these events must be pushed to the clients immediately. There are workarounds for that in AJAX, like delaying the answer to a request until there is something to report (long-polling), but these are quite dirty. That's why there are Websockets. With a websocket connection, the server can send messages to the clients when it wants and as often as it wants, without having to wait for a request from the client.

But unfortunately WebSockets also have disadvantages:

1. They aren't as well-supported by web development frameworks (yet!)
2. Not all web browsers support it ( but most desktop browsers already do )
3. Many proxies and reverse-proxies can't relay websocket traffic (yet!)

Answer 2

Actually, AJAX and websockets are two different categories. AJAX is a concept, a technique. With AJAX you can perform (as the acronym stands for) asynchronous requests, so the browser doesn't need to reload/refresh the whole page. This is good for different things, eg checking form input. Websockets are a protocol, technically quite the same as http, unless the connection will not be closed after transmition. This is good for things, where the webserver may need to contact the client (http can't do that), like a push service fore example (chat or mail client where you want to update the user interface even when the user does not refresh the page, or games). And it kills the http overhead as the whole thing has only to be done once in the beginning.

So, their for different purposes, even if they overlap. For your auto-completion I think it won't make a real difference in performance. And it even is a action/reaction thing, so the user types or submits (whatever) what can cause a request and the server responds.

Answer 3

Websockets is a powerful technology and could certainly cater for the limited use cases you;ve mentioned but there can be compatibility problems with older browsers and network intermediaries. In fact some folks even recommend having an HTTP fallback in case Websockets isn't supported.

Unless you have requirements that necessitate websockets, such as full duplex bi-directional communications for example, you might be better off using existing AJAX based solutions.

If you have requirements to push notifications to your user interface, Websockets can be a good idea, but if you are literally looking for form submission and auto-complete, then these problems have already been solved using Ajax.