CODEWITHSUNDEEP
javascriptajaxcometsynchronous
Ben
Ben

Reputation: 21

javascript COMET request onunload

I've recently taken over a project that uses COMET to perform some collaborative work and handle a simple chat room. The guys who originally wrote this thing made up some classes on top of STOMP and Oribited to handle all the actual chatting and messaging and logging.

The problem is that if a user closes the window or navigates to a different page or terminates the connection for whatever other reason, it takes a while for all the other users to see that he has logged off. The other users have to wait for the timestamp of the exited-user's last ping to exceed a certain duration before it registers that the user is no longer connected to the system.

The solution that I can think of requires sending out a notification in the onuload event that the user has left, so that it would notify all the other users without having to wait for a timeout. The problem with this is that since onunload will immediately terminate the connection before it's completed. From what I understand this is a problem with AJAX as well.

Now, I also have read that a Synchronous request in unload will delay the window-close/navigation until the request has finished.

So, my questions is this: does anyone know of a way to temporarily make the comet request synchronous in selected instances so it has time to finish the request before terminating? Or is there another way to solve this problem that I'm not thinking of? Thanks for your help.

Oh, also, onbeforeunload won't work because if it sends the request and the user selects "No, I want to stay on this page" it will have already have notified the other users that he has exited the chat.

tl;dr: Need a way to successfully fire a COMET request in the Unload event. We're using STOMP and Orbited for the COMET stuff.

Upvotes: 2

Views: 449

Answers (2)

zixtor
zixtor

Reputation: 241

The 'onbeforeunload' function produces a yes-no dialog only if some value is returned from it. So what you have to do is to use a SYNCHRONOUS XMLHttpRequest (AJAX) request inside the onbeforeunload function without returning anything. And you have to set the asynchronous flag of the request to false as seen in the AJAX GET request shown below:-

  AJAXObject.open("GET", 'http://yourdomain/logout?somevar=something', false);
    AJAXObject.send(null);

It will prevent the browser from closing until request completes and as I remember, Opera doesn't support 'onbeforeunload', so it won't work for Opera. But it works fine on IE,FF,Chrome.

Upvotes: 1

Maz
Maz

Reputation: 3375

If you are using comet, then you should control the server. The idea with comet is that it is not constant polling of the server. Every client should have a constant open connection to the server. As such, when the connection closes, the server should be able to send out a notification to the other clients.

Upvotes: 0

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