HTML page unload is not getting called always in IE - javascript

I have an onunload method written on the body of a form. Since the page got large amount contents to be streamed from the server,it takes a while to download the entire form. While the form gets downloaded to the browser,if the user clicks the window close button, the unload event (written to call a server side action to reset some flag) is not getting triggered sometimes. The unload method is written towards the end of the page, is that a reason for this? Is there anyway by which we can make sure that onunload is guaranteed to be called?

The thing that hits you is probably the fact that IE doesn't fire an unload event if window.onload hasn't fired yet. The solution is described in this blog post: http://blog.moxiecode.com/2008/04/08/unload-event-never-fires-in-ie/

There are two reasons. One, like you said, the browser may not even be reaching the unload, so you should declare it above your body tag.
The other is that, as GoldenNewby already stated, you need to give the code some time to finish, such as an alert. This is because the JavaScript is cleared from memory the moment the next page is ready, and execution is simply stopped on the old script. If you can guarantee the script will take less time than a page load, you won't need an alert, but if it could take more than 2ms or so to execute, you will need to buy some time.

IE has an onbeforeunload event, you can use that instead. Just set a flag so that your onunload can exit early if onbeforeunload already did its thing.
window.onunload = window.onbeforeunload = function () {
if (window.isAlreadyUnloaded) return;
window.isAlreadyUnloaded = true;
// do your stuff here.
}

Related

Vaadin onbeforeunload event

Is there any Out Of the Box Vaadin 10 (and higher) event similar to window.onbeforeunload in JavaScript?
I've tried to use onDetach() or beforeLeave(), but it only works inside UI, and when user reloads the page or closes the page it's not working.
You can use the approach described in https://vaadin.com/forum/thread/17523194/unsaved-changes-detect-page-exit-or-reload that was already suggested in a comment.
At the same time, I'd urge you to be really careful with beforeunload events since they are in some situations fired even though the user is actually not navigating away from the page.
The most common case is if the user clicks a link that starts a download. In that case the browser will fire the event immediately when the user clicks the link. Slightly later when the browser receives the response headers, it will discover that it's a download and not a new HTML page to display. The end result is then that beforeunload has been fired but the previous page is still kept running.
If you want to use the event for cleanup, then the best approach today is probably a combination of the unload event and then using the new-ish Beacon API for notifying the server that the user has actually navigated away. Integrating this into a Vaadin application will require slightly more JavaScript, but it has the benefit that it will actually work.

Javascript event that runs before page changes

Is there such a thing?
I know that I can hook my function on the click event of all links, but there are other situations where a page is changed, like refresh or when a different script changes the window.location
In the end, I did it by sending a string trough postMessage from the unload event, like this:
$(window).bind('unload', function(e){
window.parent.postMessage('unloading');
});
in the parent document:
$(window).bind('message', function(e){
if(e.originalEvent.data == 'unloading'){
// ajax stuff here
}
});
It appears to work.
I probably should have mentioned that there's a iframe involved :)
There's the beforeunload event, which is fired when the page is being torn down (either to follow a link, or if the window is being closed, or refresh, etc.). Example:
window.onbeforeunload = function(event) {
var s = "You have unsaved changes. Really leave?";
event = event || window.event;
if (event) {
// This is for IE
event.returnValue = s;
}
// This is for all other browsers
return s;
}
There are, for obvious reasons, very strict limits on what you can do in the handler of the beforeunload event, and as you can see above beforeunload handlers have a different signature than normal event handlers. Basically, your code can't do anything asynchronous, can't open new windows, and can't cancel the event. It can return a string, and if it does, the browser will pop up a window asking whether you really want to leave the page, and including your string in that pop-up.
From your comment on the question:
I need it before so I can fire a ajax request and update some things...
The way to do that here many years after the question was originally asked is with the beacon API. This lets you send a non-blocking asynchronous request to the server without slowing down the process of the browser tearing down your page and navigating to the next:
navigator.sendBeacon("/path/to/notify", optionalData);
It's a send-and-forget, but the browser doesn't cancel it when your page is torn down (like it does a standard asynchronous ajax request). Instead, it allows that request to complete even though your page has been removed.
Back in 2012 when this answer was originally written, you could usually get away with a synchronous ajax call (async: false) provided it didn't take too long. But you can't reliably do that now (and it was never a good idea, it holds up the UI).
jQuery has unload function:
The unload event is sent to the window element when the user navigates
away from the page. This could mean one of many things. The user could
have clicked on a link to leave the page, or typed in a new URL in the
address bar. The forward and back buttons will trigger the event.
Closing the browser window will cause the event to be triggered. Even
a page reload will first create an unload event.
Note that this should be binded to window object instead of document:
$(window).unload(function() {
// do something
});
You can also bind handler to beforeunload event:
$(window).bind('beforeunload', function() {
// do something, preferably ajax request etc
return 'are you sure?';
});
When a page is reloaded, whatever was there before will be gone. Thus, it seems like what you're talking about is something you'd do at DOMReady or "load" in the new page, since you can't "push" code from the former page into the new context.

DOM onUnload doesn't fire until response begins

Consider the following code:
$(window).unload(function () {
console.log('foo');
});
If I trigger the unload event by navigating to a different URL, the event doesn't fire until the browser begins to get a response.
i.e. if the DNS lookup takes a long time, or the remote server takes time to respond (the loader animating anti-clockwise in Firefox, the event only fires once it starts rotating clockwise)
Is there another event I can listen to that happens as soon as navigation begins?
I realise I could attach to link clicks and intercept there, but that's just going to be hacky because there countless edge cases I'd have to manually capture here. OnUnload is the sensible place, but it doesn't behave as I want :(
thoughts?
There's window.onbeforeunload that might do what you're looking for.

Chrome/Safari not calling unload in some cases

Have been stuck with this issue for a few days now, and really need, and would appreciate some help. My requirement is that I want to make a server side callback to clear off some objects when the user navigates away from our page, without clicking logout. For business reasons, our ASP.NET session timeout has to be set to a very high value. Further, I do not want to popup a alert/dialog to force the user to return to the page and click Logoff.
The solution I have arrived at thus far is to make a AJAX callback by embedding this javascript in the page.
window.onunload = pageleave;
function pageleave() {
alert('test');
PageMethods.CheckLogout('abc','xyz',OnSucceed,OnFail);
}
Here is the problem though :
For IE and Firefox, the unload fires, the alert is seen, and I see the callback on my C# side in all the cases I desire
a) User closes browser
b) User types in a new URL in the address bar
c) User clicks on a link causing page to reload
For Chrome and Safari, cases a and b work fine. However, when the user clicks on a link, which causes my aspx page to reload, my C# side code is not invoked. The javasacript alert is fired though.
I am trying to see how I can get Chrome/Safari to behave like IE/Firefox. Is this even a possibility?
Thanks in advance for the help,
Rajesh.
Use the beforeunload event instead of the unload event.
Also, use a synchronous AJAX request, not an asynchronous one, so that the request is completed before your beforeunload function exits.
I'm not sure how you would do a synchronous AJAX request using your JavaScript framework. In jQuery, it would look like this:
window.onbeforeunload = function() {
jQuery.ajax({
url: '/page/to/load',
async: false
});
};
In case anyone comes across this in the future, I couldn't use window.onbeforeunload as it was firing too early. Instead, I found window.onpagehide as a suitable workaround.
e.g.
window.onpagehide = function() {
// some code here.
};

How can I get reason of page unloading in javascript's onunload event, in IE?

There may be different reasons of page unloading:
1 User closes the current window.
2 User navigates to another location.
3 Clicks the Back, Forward, Refresh, or Home button.
4 User submits a form, and then browser starts to unload current page and load page with results of form submitting. (Assuming that the current window is the form's target).
5 and so on...
Can I somehow know in onunload handler that the reason of unloading is p.4, i.e. moving to page with results of form submitting?
I could define some flag when submiting form, but this does not solve the problem. Because response (on form submit) from web server takes some time, browser doesn't unload the current page immediately and waits response from server. And during this waiting user may close window or navigate anywhere. And I need to know whether was it indeed moving to results page or something else...?
You could hijack some of those events.
For example for links, you could add an event handler on links that saves their href attribute, performs what you require, then sets window.location to the href you had stored in a variable.
The exact reason of page unload cannot be known in the unload handler. OnUnload event is not a standard and was implemented by IE first.
Different browsers might handle it differently and fire the event for different cases.
msdn reference
mozilla reference
So if you are trying to know the reason of unload in the unload handler, I think you might be out of luck. However as Alex pointed out in his answer, you could probably know about user navigating away from your page by clicking some link on your page by making your click handlers for those links more intelligent.
on unload cant handle its looks like but maybe when load you can handle.
as explained
performance.getEntriesByType("navigation")[0].type
You can check this Link
What is the replacement for performance.navigation.type in angular?

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