Perform disconnect on unload rather than beforeunload

[Kequc]

Ref: #49

Frees up beforeunload event for use by developer. For example to display a warning to the user that they are leaving the page and will lose their connection.

[jondubois]

@Kequc Hmmm, that solution is not ideal. The unload event is not as reliable as beforeunload (in several browsers. See http://stackoverflow.com/questions/4376596/jquery-unload-or-beforeunload) - This means that the server would get a lot of 'Socket Hung Up' issues because the clients would not disconnect correctly when the user navigates to a different page (for example).

Socket.io uses the same technique as we do currently. See https://github.com/socketio/socket.io-client/blob/master/socket.io.js#L3663

To solve your use case, we could add an extra option when creating the socket client:

socketCluster.connect({
  // ...
  disconnectOnUnload: true
});

true would be the default, but in your case you could set it to false... Then, it would be your responsibility to call socket.disconnect() when the user leaves the page.

[Kequc]

I see. It seemed that because the attachEvent method was using unload, it made more sense and was a typo. I guess I was wrong. That feature would be desirable.

[jondubois]

Yep, the attachEvent is for IE, which is better at handling the unload event. When I tested it (a while ago) I think the issue with the unload event affected Firefox.

[jondubois]

I'll make the fix for you now.

[Kequc]

ooh! I was gonna go do it. Thanks.

[jondubois]

@Kequc Ok, v5.0.9 has the fix https://www.npmjs.com/package/socketcluster-client - You can just pass the disconnectOnUnload: false option.

[Kequc]

How do I know if the user blocked page unload? In your opinion where should I place my disconnect statement here?

window.addEventListener('beforeunload', (e) => {
    let message = "Your connection will be interrupted.";
    e.returnValue = message;
    return message;
});

Thanks for the code update!

[jondubois]

@Kequc Not sure, it depends how you want to implement it.

[Kequc]

It seems... Not possible with the current solution. There isn't a way to know whether the user clicked "ok" in the resulting dialog. They are simply and immediately taken off the page, this is in order to prevent abuse by websites that would rather you are unable to navigate away.

Therefore, with disconnectonunload disabled, navigating away from the page always results in socket hung up errors unfortunately.

For reference: (beforeunload)[https://developer.mozilla.org/en/docs/Web/Events/beforeunload]