Question

If I make a AJAX reqeust it will be displayed in the network tab in Chrome. If I in the same moment makes a client based redirect, the AJAX request will canceled. But will the request make it to the server and execute as normal? Is it something in HTTP/TCP that know’s that the client has canceled the request? I don’t think so, but I want to be sure.

Answer 1

If you’re running PHP server-side, it will stop processing in the event of a client-side abort. (From what I’ve read, this isn’t the case with other server-side technologies, which will continue processing after a client aborts.) See:

http://php.net/manual/en/features.connection-handling.php

But, it’s best not to assume anything one way or another. The browser may cancel the request. And this cancellation may occur in time to stop processing server-side. But, that’s not necessarily the case. The client could cancel at any stage during the request — from right before the request is actually sent to just after a response body is sent. Also bear in mind, there are other things which can interrupt server-side request processing (hardware, power, OS failure, etc.). Expect some unpredictability.

From this, I’d make two recommendations:

• Write your code be as transaction-safe as possible. If a request makes data changes, don’t commit them until all changes have been piped to the database. And if your application relies on multiple AJAX requests to change some data, don’t commit any of the changes until the the end of “final” AJAX request.

• Do not assume, even if a request finishes, that the client receives the response. Off the top of my head, that means if your application is AJAX-heavy, always rely on client-side state to tell the server what information it has, rather than relying on server-side state to assume the client “knows” something.