Develop Reference

How do I use a custom confirmation method when window.onbeforeunload happens [duplicate]

I need to warn users about unsaved changes before they leave a page (a pretty common problem).
window.onbeforeunload = handler
This works but it raises a default dialog with an irritating standard message that wraps my own text. I need to either completely replace the standard message, so my text is clear, or (even better) replace the entire dialog with a modal dialog using jQuery.
So far I have failed and I haven't found anyone else who seems to have an answer. Is it even possible?
Javascript in my page:
<script type="text/javascript">
window.onbeforeunload = closeIt;
</script>
The closeIt() function:
function closeIt()
{
if (changes == "true" || files == "true")
{
return "Here you can append a custom message to the default dialog.";
}
}
Using jQuery and jqModal I have tried this kind of thing (using a custom confirm dialog):
$(window).beforeunload(function () {
confirm('new message: ' + this.href + ' !', this.href);
return false;
});
which also doesn't work - I cannot seem to bind to the beforeunload event.

You can't modify the default dialogue for onbeforeunload, so your best bet may be to work with it.
window.onbeforeunload = function() {
return 'You have unsaved changes!';
}
Here's a reference to this from Microsoft:
When a string is assigned to the returnValue property of window.event, a dialog box appears that gives users the option to stay on the current page and retain the string that was assigned to it. The default statement that appears in the dialog box, "Are you sure you want to navigate away from this page? ... Press OK to continue, or Cancel to stay on the current page.", cannot be removed or altered.
The problem seems to be:
When onbeforeunload is called, it will take the return value of the handler as window.event.returnValue.
It will then parse the return value as a string (unless it is null).
Since false is parsed as a string, the dialogue box will fire, which will then pass an appropriate true/false.
The result is, there doesn't seem to be a way of assigning false to onbeforeunload to prevent it from the default dialogue.
Additional notes on jQuery:
Setting the event in jQuery may be problematic, as that allows other onbeforeunload events to occur as well. If you wish only for your unload event to occur I'd stick to plain ol' JavaScript for it.
jQuery doesn't have a shortcut for onbeforeunload so you'd have to use the generic bind syntax.
$(window).bind('beforeunload', function() {} );
Edit 09/04/2018: custom messages in onbeforeunload dialogs are deprecated since chrome-51 (cf: release note)

What worked for me, using jQuery and tested in IE8, Chrome and Firefox, is:
$(window).bind("beforeunload",function(event) {
if(hasChanged) return "You have unsaved changes";
});
It is important not to return anything if no prompt is required as there are differences between IE and other browser behaviours here.

While there isn't anything you can do about the box in some circumstances, you can intercept someone clicking on a link. For me, this was worth the effort for most scenarios and as a fallback, I've left the unload event.
I've used Boxy instead of the standard jQuery Dialog, it is available here: http://onehackoranother.com/projects/jquery/boxy/
$(':input').change(function() {
if(!is_dirty){
// When the user changes a field on this page, set our is_dirty flag.
is_dirty = true;
}
});
$('a').mousedown(function(e) {
if(is_dirty) {
// if the user navigates away from this page via an anchor link,
// popup a new boxy confirmation.
answer = Boxy.confirm("You have made some changes which you might want to save.");
}
});
window.onbeforeunload = function() {
if((is_dirty)&&(!answer)){
// call this if the box wasn't shown.
return 'You have made some changes which you might want to save.';
}
};
You could attach to another event, and filter more on what kind of anchor was clicked, but this works for me and what I want to do and serves as an example for others to use or improve. Thought I would share this for those wanting this solution.
I have cut out code, so this may not work as is.

1) Use onbeforeunload, not onunload.
2) The important thing is to avoid executing a return statement. I don't mean, by this, to avoid returning from your handler. You return all right, but you do it by ensuring that you reach the end of the function and DO NOT execute a return statement. Under these conditions the built-in standard dialog does not occur.
3) You can, if you use onbeforeunload, run an ajax call in your unbeforeunload handler to tidy up on the server, but it must be a synchronous one, and you have to wait for and handle the reply in your onbeforeunload handler (still respecting condition (2) above). I do this and it works fine. If you do a synchronous ajax call, everything is held up until the response comes back. If you do an asynchronous one, thinking that you don't care about the reply from the server, the page unload continues and your ajax call is aborted by this process - including a remote script if it's running.

This can't be done in chrome now to avoid spamming, refer to javascript onbeforeunload not showing custom message for more details.

Angular 9 approach:
constructor() {
window.addEventListener('beforeunload', (event: BeforeUnloadEvent) => {
if (this.generatedBarcodeIndex) {
event.preventDefault(); // for Firefox
event.returnValue = ''; // for Chrome
return '';
}
return false;
});
}
Browsers support and the removal of the custom message:
Chrome removed support for the custom message in ver 51 min
Opera removed support for the custom message in ver 38 min
Firefox removed support for the custom message in ver 44.0 min
Safari removed support for the custom message in ver 9.1 min

Try placing a return; instead of a message.. this is working most browsers for me.
(This only really prevents dialog's presents)
window.onbeforeunload = function(evt) {
//Your Extra Code
return;
}

You can detect which button (ok or cancel) pressed by user, because the onunload function called only when the user choise leaveing the page. Althoug in this funcion the possibilities is limited, because the DOM is being collapsed. You can run javascript, but the ajax POST doesn't do anything therefore you can't use this methode for automatic logout. But there is a solution for that. The window.open('logout.php') executed in the onunload funcion, so the user will logged out with a new window opening.
function onunload = (){
window.open('logout.php');
}
This code called when user leave the page or close the active window and user logged out by 'logout.php'.
The new window close immediately when logout php consist of code:
window.close();

I faced the same problem, I was ok to get its own dialog box with my message, but the problem I faced was :
1) It was giving message on all navigations I want it only for close click.
2) with my own confirmation message if user selects cancel it still shows the browser's default dialog box.
Following is the solutions code I found, which I wrote on my Master page.
function closeMe(evt) {
if (typeof evt == 'undefined') {
evt = window.event; }
if (evt && evt.clientX >= (window.event.screenX - 150) &&
evt.clientY >= -150 && evt.clientY <= 0) {
return "Do you want to log out of your current session?";
}
}
window.onbeforeunload = closeMe;

<script type="text/javascript">
window.onbeforeunload = function(evt) {
var message = 'Are you sure you want to leave?';
if (typeof evt == 'undefined') {
evt = window.event;
}
if (evt) {
evt.returnValue = message;
}
return message;
}
</script>
refer from http://www.codeprojectdownload.com

What about to use the specialized version of the "bind" command "one". Once the event handler executes the first time, it’s automatically removed as an event handler.
$(window).one("beforeunload", BeforeUnload);

Try this
$(window).bind('beforeunload', function (event) {
setTimeout(function () {
var retVal = confirm("Do you want to continue ?");
if (retVal == true) {
alert("User wants to continue!");
return true;
}
else {
window.stop();
return false;
}
});
return;
});

beforeunload() event to be triggered only when window/tab closed but not on any other condition [duplicate]

I need to warn users about unsaved changes before they leave a page (a pretty common problem).
window.onbeforeunload = handler
This works but it raises a default dialog with an irritating standard message that wraps my own text. I need to either completely replace the standard message, so my text is clear, or (even better) replace the entire dialog with a modal dialog using jQuery.
So far I have failed and I haven't found anyone else who seems to have an answer. Is it even possible?
Javascript in my page:
<script type="text/javascript">
window.onbeforeunload = closeIt;
</script>
The closeIt() function:
function closeIt()
{
if (changes == "true" || files == "true")
{
return "Here you can append a custom message to the default dialog.";
}
}
Using jQuery and jqModal I have tried this kind of thing (using a custom confirm dialog):
$(window).beforeunload(function () {
confirm('new message: ' + this.href + ' !', this.href);
return false;
});
which also doesn't work - I cannot seem to bind to the beforeunload event.

You can't modify the default dialogue for onbeforeunload, so your best bet may be to work with it.
window.onbeforeunload = function() {
return 'You have unsaved changes!';
}
Here's a reference to this from Microsoft:
When a string is assigned to the returnValue property of window.event, a dialog box appears that gives users the option to stay on the current page and retain the string that was assigned to it. The default statement that appears in the dialog box, "Are you sure you want to navigate away from this page? ... Press OK to continue, or Cancel to stay on the current page.", cannot be removed or altered.
The problem seems to be:
When onbeforeunload is called, it will take the return value of the handler as window.event.returnValue.
It will then parse the return value as a string (unless it is null).
Since false is parsed as a string, the dialogue box will fire, which will then pass an appropriate true/false.
The result is, there doesn't seem to be a way of assigning false to onbeforeunload to prevent it from the default dialogue.
Additional notes on jQuery:
Setting the event in jQuery may be problematic, as that allows other onbeforeunload events to occur as well. If you wish only for your unload event to occur I'd stick to plain ol' JavaScript for it.
jQuery doesn't have a shortcut for onbeforeunload so you'd have to use the generic bind syntax.
$(window).bind('beforeunload', function() {} );
Edit 09/04/2018: custom messages in onbeforeunload dialogs are deprecated since chrome-51 (cf: release note)

What worked for me, using jQuery and tested in IE8, Chrome and Firefox, is:
$(window).bind("beforeunload",function(event) {
if(hasChanged) return "You have unsaved changes";
});
It is important not to return anything if no prompt is required as there are differences between IE and other browser behaviours here.

While there isn't anything you can do about the box in some circumstances, you can intercept someone clicking on a link. For me, this was worth the effort for most scenarios and as a fallback, I've left the unload event.
I've used Boxy instead of the standard jQuery Dialog, it is available here: http://onehackoranother.com/projects/jquery/boxy/
$(':input').change(function() {
if(!is_dirty){
// When the user changes a field on this page, set our is_dirty flag.
is_dirty = true;
}
});
$('a').mousedown(function(e) {
if(is_dirty) {
// if the user navigates away from this page via an anchor link,
// popup a new boxy confirmation.
answer = Boxy.confirm("You have made some changes which you might want to save.");
}
});
window.onbeforeunload = function() {
if((is_dirty)&&(!answer)){
// call this if the box wasn't shown.
return 'You have made some changes which you might want to save.';
}
};
You could attach to another event, and filter more on what kind of anchor was clicked, but this works for me and what I want to do and serves as an example for others to use or improve. Thought I would share this for those wanting this solution.
I have cut out code, so this may not work as is.

1) Use onbeforeunload, not onunload.
2) The important thing is to avoid executing a return statement. I don't mean, by this, to avoid returning from your handler. You return all right, but you do it by ensuring that you reach the end of the function and DO NOT execute a return statement. Under these conditions the built-in standard dialog does not occur.
3) You can, if you use onbeforeunload, run an ajax call in your unbeforeunload handler to tidy up on the server, but it must be a synchronous one, and you have to wait for and handle the reply in your onbeforeunload handler (still respecting condition (2) above). I do this and it works fine. If you do a synchronous ajax call, everything is held up until the response comes back. If you do an asynchronous one, thinking that you don't care about the reply from the server, the page unload continues and your ajax call is aborted by this process - including a remote script if it's running.

This can't be done in chrome now to avoid spamming, refer to javascript onbeforeunload not showing custom message for more details.

Angular 9 approach:
constructor() {
window.addEventListener('beforeunload', (event: BeforeUnloadEvent) => {
if (this.generatedBarcodeIndex) {
event.preventDefault(); // for Firefox
event.returnValue = ''; // for Chrome
return '';
}
return false;
});
}
Browsers support and the removal of the custom message:
Chrome removed support for the custom message in ver 51 min
Opera removed support for the custom message in ver 38 min
Firefox removed support for the custom message in ver 44.0 min
Safari removed support for the custom message in ver 9.1 min

Try placing a return; instead of a message.. this is working most browsers for me.
(This only really prevents dialog's presents)
window.onbeforeunload = function(evt) {
//Your Extra Code
return;
}

You can detect which button (ok or cancel) pressed by user, because the onunload function called only when the user choise leaveing the page. Althoug in this funcion the possibilities is limited, because the DOM is being collapsed. You can run javascript, but the ajax POST doesn't do anything therefore you can't use this methode for automatic logout. But there is a solution for that. The window.open('logout.php') executed in the onunload funcion, so the user will logged out with a new window opening.
function onunload = (){
window.open('logout.php');
}
This code called when user leave the page or close the active window and user logged out by 'logout.php'.
The new window close immediately when logout php consist of code:
window.close();

I faced the same problem, I was ok to get its own dialog box with my message, but the problem I faced was :
1) It was giving message on all navigations I want it only for close click.
2) with my own confirmation message if user selects cancel it still shows the browser's default dialog box.
Following is the solutions code I found, which I wrote on my Master page.
function closeMe(evt) {
if (typeof evt == 'undefined') {
evt = window.event; }
if (evt && evt.clientX >= (window.event.screenX - 150) &&
evt.clientY >= -150 && evt.clientY <= 0) {
return "Do you want to log out of your current session?";
}
}
window.onbeforeunload = closeMe;

<script type="text/javascript">
window.onbeforeunload = function(evt) {
var message = 'Are you sure you want to leave?';
if (typeof evt == 'undefined') {
evt = window.event;
}
if (evt) {
evt.returnValue = message;
}
return message;
}
</script>
refer from http://www.codeprojectdownload.com

What about to use the specialized version of the "bind" command "one". Once the event handler executes the first time, it’s automatically removed as an event handler.
$(window).one("beforeunload", BeforeUnload);

Try this
$(window).bind('beforeunload', function (event) {
setTimeout(function () {
var retVal = confirm("Do you want to continue ?");
if (retVal == true) {
alert("User wants to continue!");
return true;
}
else {
window.stop();
return false;
}
});
return;
});

Javascript confirmation cancel button issue [duplicate]

In my Rails 3 application I do:
render :js => "alert(\"Error!\\nEmpty message sent.\");" if ...
Sometimes, below this error message (in the same alert box) I see: "Prevent this page from creating additional dialogs" and a checkbox.
What does this mean ?
Is that possible not to display this additional text and checkbox ?
I use Firefox 4.

It's a browser feature to stop websites that show annoying alert boxes over and over again.
As a web developer, you can't disable it.

What does this mean ?
This is a security measure on the browser's end to prevent a page from freezing the browser (or the current page) by showing modal (alert / confirm) messages in an infinite loop. See e.g. here for Firefox.
You can not turn this off. The only way around it is to use custom dialogs like JQuery UI's dialogs.

You can create a custom alert box using java script, below code will override default alert function
window.alert = function(message) { $(document.createElement('div'))
.attr({
title: 'Alert',
'class': 'alert'
})
.html(message)
.dialog({
buttons: {
OK: function() {
$(this).dialog('close');
}
},
close: function() {
$(this).remove();
},
modal: true,
resizable: false,
width: 'auto'
});
};

Using JQuery UI's dialogs is not always a solution. As far as I know alert and confirm is the only way to stop the execution of a script at a certain point. As a workaround we can provide a mechanism to let the user know that an application needs to call alert and confirm. This can be done like this for example (where showError uses a jQuery dialog or some other means to communicate with the user):
var f_confirm;
function setConfirm() {
f_confirm = confirm;
confirm = function(s) {
try {
return f_confirm(s);
} catch(e) {
showError("Please do not check 'Prevent this page from creating additional dialogs'");
}
return false;
};
};

I designed this function to hopefully circumvent the checkbox in my web apps.
It blocks all functionality on the page while executing (assuming fewer than three seconds has passed since the user closed the last dialog), but I prefer it to a recursive or setTimeout function since I don't have to code for the possibility of something else being clicked or triggered while waiting for the dialog to appear.
I require it most when displaying errors/prompts/confirms on reports that are already contained within Modalbox. I could add a div for additional dialogs, but that just seems too messy and unnecessary if built-in dialogs can be used.
Note that this would probably break if dom.successive_dialog_time_limit is changed to a value greater than 3, nor do I know if Chrome has the the same default as Firefox. But at least it's an option.
Also, if anyone can improve upon it, please do!
// note that these should not be in the global namespace
var dlgRslt,
lastTimeDialogClosed = 0;
function dialog(msg) {
var defaultValue,
lenIsThree,
type;
while (lastTimeDialogClosed && new Date() - lastTimeDialogClosed < 3001) {
// timer
}
lenIsThree = 3 === arguments.length;
type = lenIsThree ? arguments[2] : (arguments[1] || alert);
defaultValue = lenIsThree && type === prompt ? arguments[1] : '';
// store result of confirm() or prompt()
dlgRslt = type(msg, defaultValue);
lastTimeDialogClosed = new Date();
}
usage:
dialog('This is an alert.');
dialog( 'This is a prompt', prompt );
dialog('You entered ' + dlgRslt);
dialog( 'Is this a prompt?', 'maybe', prompt );
dialog('You entered ' + dlgRslt);
dialog( 'OK/Cancel?', confirm );
if (dlgRslt) {
// code if true
}

This is a browser feature.
If you could, try to employ http://bootboxjs.com/, whit this library you can do the same of
alert("Empty message sent");
by writing:
bootbox.alert("Empty message sent", function(result) {
// do something whit result
});
You'll get a nice user interface too!

Disable the checkbox in "Prevent this page creating additional dialogs" ( Javascript alert ) [duplicate]

In my Rails 3 application I do:
render :js => "alert(\"Error!\\nEmpty message sent.\");" if ...
Sometimes, below this error message (in the same alert box) I see: "Prevent this page from creating additional dialogs" and a checkbox.
What does this mean ?
Is that possible not to display this additional text and checkbox ?
I use Firefox 4.

It's a browser feature to stop websites that show annoying alert boxes over and over again.
As a web developer, you can't disable it.

What does this mean ?
This is a security measure on the browser's end to prevent a page from freezing the browser (or the current page) by showing modal (alert / confirm) messages in an infinite loop. See e.g. here for Firefox.
You can not turn this off. The only way around it is to use custom dialogs like JQuery UI's dialogs.

You can create a custom alert box using java script, below code will override default alert function
window.alert = function(message) { $(document.createElement('div'))
.attr({
title: 'Alert',
'class': 'alert'
})
.html(message)
.dialog({
buttons: {
OK: function() {
$(this).dialog('close');
}
},
close: function() {
$(this).remove();
},
modal: true,
resizable: false,
width: 'auto'
});
};

Using JQuery UI's dialogs is not always a solution. As far as I know alert and confirm is the only way to stop the execution of a script at a certain point. As a workaround we can provide a mechanism to let the user know that an application needs to call alert and confirm. This can be done like this for example (where showError uses a jQuery dialog or some other means to communicate with the user):
var f_confirm;
function setConfirm() {
f_confirm = confirm;
confirm = function(s) {
try {
return f_confirm(s);
} catch(e) {
showError("Please do not check 'Prevent this page from creating additional dialogs'");
}
return false;
};
};

I designed this function to hopefully circumvent the checkbox in my web apps.
It blocks all functionality on the page while executing (assuming fewer than three seconds has passed since the user closed the last dialog), but I prefer it to a recursive or setTimeout function since I don't have to code for the possibility of something else being clicked or triggered while waiting for the dialog to appear.
I require it most when displaying errors/prompts/confirms on reports that are already contained within Modalbox. I could add a div for additional dialogs, but that just seems too messy and unnecessary if built-in dialogs can be used.
Note that this would probably break if dom.successive_dialog_time_limit is changed to a value greater than 3, nor do I know if Chrome has the the same default as Firefox. But at least it's an option.
Also, if anyone can improve upon it, please do!
// note that these should not be in the global namespace
var dlgRslt,
lastTimeDialogClosed = 0;
function dialog(msg) {
var defaultValue,
lenIsThree,
type;
while (lastTimeDialogClosed && new Date() - lastTimeDialogClosed < 3001) {
// timer
}
lenIsThree = 3 === arguments.length;
type = lenIsThree ? arguments[2] : (arguments[1] || alert);
defaultValue = lenIsThree && type === prompt ? arguments[1] : '';
// store result of confirm() or prompt()
dlgRslt = type(msg, defaultValue);
lastTimeDialogClosed = new Date();
}
usage:
dialog('This is an alert.');
dialog( 'This is a prompt', prompt );
dialog('You entered ' + dlgRslt);
dialog( 'Is this a prompt?', 'maybe', prompt );
dialog('You entered ' + dlgRslt);
dialog( 'OK/Cancel?', confirm );
if (dlgRslt) {
// code if true
}

This is a browser feature.
If you could, try to employ http://bootboxjs.com/, whit this library you can do the same of
alert("Empty message sent");
by writing:
bootbox.alert("Empty message sent", function(result) {
// do something whit result
});
You'll get a nice user interface too!

JavaScript confirmation window always returning false on Safari for iPhone

I'm using Knockout.JS to power a form and I have a button that when pressed displays a confirmation window. Only on Safari for iPhone it always returns false. It works with Chrome on my iPhone, and on my iPad and laptop it works on all browsers(including Safari). There are no errors either.
self.submitPayment = function(){
var errors2 = ko.validation.group(secondValidationGroup);
if (errors2().length == 0) {
if(confirm_reservation() == true){
finalizePayment(); //calls function which displays a new div
}
else{
alert('False was returned'); //displays before I even make a selection
}
}
else{
errors2.showAllMessages();
}
}
//used to confirm submission for submitPayment
function confirm_reservation(){
var conf = confirm('Click OK to submit your payment');
return conf;
}
Before I even make a selection, I get the 'False was returned' alert. So basically it's not even letting me make a selection before it returns the value.
edit - It is now working and I think I may have encountered a bug
I cleared my cookies/cache on my phone and restarted it and then it proceeded to work properly.

You may try:
if(confirm('Your question'))
{
// do things if OK
}
else
{
// do things if KO
}

After AOZ suggested that it may have been a bug, I cleared my cookies/cache and restarted my phone and then it proceeded to work. I am using my original method and it now works properly.

I think the problem due the asycnhronus things, your "confirm_reservation" method doesnot wait the confirm result, and return false directly.. Can you try below confirm block changing with yours.
confirm('Click OK to submit your payment', function(result) {
if(result) {
finalizePayment();
} else {
alert('False was returned'); //displays before I even make a selection
}
});