How to cancel a window unload?

[gregerly]

I'm working on a corporate intranet site and am trying to create a page that will warn a user on window unload if they have not saved thier work. Basically I just select all inputs, and on change, set var changes = true; On window unload if changes==true, they have made changes that are not yet saved, and I want a confirm box to pop up, asking if they really want to leave or stay on the page? At this point is it to late to cancel the window unload? My code is below:

window.onunload=checkChanges;
var changes=false;
 
function checkChanges(){
    if(changes==true){//changes have been made
        if(!confirm("Do you want to leave without saving your changes?\n\nOK to Go, Cancel to stay on this page.")){
                window.unload=false;
        }
    }
}
 
//while looping thru all inputs
        inputs[x].onchange=function(){
            changes=true;
        };

I'm getting the proper confirm boxes, but I dont' know how to cancel the unload, if it's even possible.

Thanks,

Greg

[mrhoo]

try onbeforeunload.

window.onbeforeunload= function(){
    return 'You are about to leave this page, OK?';
};

[gregerly]

try onbeforeunload.

window.onbeforeunload= function(){
    return 'You are about to leave this page, OK?';
};

Thanks alot mrhoo. That worked great. I had some other questions, but I just got it figued out. Apparently the onbeforeunload prompts with it's own confirm that will keep a user on the page. Found that in this thread.

Thanks again!