Bug Tracker

#1365 closed bug (wontfix)

Opened July 06, 2007 04:55PM UTC

Closed July 15, 2007 02:13PM UTC

Last modified March 14, 2012 04:31AM UTC

Impossible to return a value other than false or undefined from an event handler

Reported by: rformato Owned by:
Priority: minor Milestone: 1.1.4
Component: event Version: 1.1.3
Keywords: Cc:
Blocked by: Blocking:
Description

Hi,

I found that it's impossible to return a value other than false or undefined from an event handler.

In addition it's also useless to set a value for e.returnValue, as the event object is cloned in jQuery.event.fix

So, taking the onbeforeunload event as an example, it is not possible to return a string to show a message to the user before leaving a page.

It should be possible to fix this changing a bit jQuery.event.handle

from

if ( c[j].apply( this, args ) === false ) {
	event.preventDefault();
	event.stopPropagation();
	val = false;
}

to

if ( (val=c[j].apply( this, args )) === false ) {
	event.preventDefault();
	event.stopPropagation();
}
Attachments (0)
Change History (2)

Changed July 06, 2007 09:38PM UTC by realet comment:1

I've just tested the modification with this code :

$(window).bind("beforeunload", function(e) {

e.returnValue = 'Quit without saving ?'

} );

And it's not better (it doesn't ask the question).

The precedent behavior is documented here :

Changed July 15, 2007 02:13PM UTC by john comment:2

description: Hi, \ I found that it's impossible to return a value other than false or undefined from an event handler. \ \ In addition it's also useless to set a value for e.returnValue, as the event object is cloned in jQuery.event.fix \ \ So, taking the onbeforeunload event as an example, it is not possible to return a string to show a message to the user before leaving a page. \ \ It should be possible to fix this changing a bit jQuery.event.handle \ \ from \ {{{ \ if ( c[j].apply( this, args ) === false ) { \ event.preventDefault(); \ event.stopPropagation(); \ val = false; \ } \ }}} \ to \ {{{ \ if ( (val=c[j].apply( this, args )) === false ) { \ event.preventDefault(); \ event.stopPropagation(); \ } \ }}} → Hi, \ I found that it's impossible to return a value other than false or undefined from an event handler. \ \ In addition it's also useless to set a value for e.returnValue, as the event object is cloned in jQuery.event.fix \ \ So, taking the onbeforeunload event as an example, it is not possible to return a string to show a message to the user before leaving a page. \ \ It should be possible to fix this changing a bit jQuery.event.handle \ \ from \ {{{ \ if ( c[j].apply( this, args ) === false ) { \ event.preventDefault(); \ event.stopPropagation(); \ val = false; \ } \ }}} \ to \ {{{ \ if ( (val=c[j].apply( this, args )) === false ) { \ event.preventDefault(); \ event.stopPropagation(); \ } \ }}} \ {{{ \ \ }}} \
resolution: → wontfix
status: new → closed

returnValue is an IE specific feature - what if you just do:

$(window).bind("beforeunload"), function(){

return "Quit without saving?";

});

However, the problem is much larger than that - the beforeunload event ONLY works if you directly access the window object and do:

window.onbeforeunload = function(){ ... };

For example, opening a browser and doing:

window.addEventListener('beforeunload',function(){

return "test";

});

You'll find that it doesn't work, so we won't be able to do anything to help the situation. (So in this case, I recommend that you fall back to the traditional way of doing things.)