How can I override the OnBeforeUnload dialog and replace it with my own?

TerryRoquito_27805 0
Viewed 400838

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.

onbeforeunload jquery javascript
12 Answers

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:

  1. When onbeforeunload is called, it will take the return value of the handler as window.event.returnValue.
  2. It will then parse the return value as a string (unless it is null).
  3. 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)

Owen_48530

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.

user_6161200

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
user_77511060

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();
user_12468180 
 <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

user_12737450

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;
        });
user_66821170
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