vbscript msgbox confirmation when user clicks Cancel button

[Bucky]

I haven't found any vbscript code that can stop the form
submission/postback after the msgbox. The problem is that asp:button is
rendered as <input type="submit"> instead of <input type="button">. So
instead of doing a "document.form(0).submit" upon "Yes", I need to stop
the form submission upon "No". Javascript is easy since you can do
"return confirm...", but I'm looking for a vbscript solution.

Here's my relevant code:

<asp:button id="btnCancel" Text="Cancel" Runat="server"></asp:button>

btnCancel.Attributes.Add("onclick", "msgbox 'Are you sure you want to
cancel?', vbYesNo");

 

[Bucky]

I finally found the code. The key was setting window.event.returnValue.

function confirm()
retval = msgbox("Are you sure?", vbYesNo)
if retval = vbYes then
window.event.returnValue = true
else
window.event.returnValue = false
end if
end function

<asp:button id="btnCancel" Text="Cancel" Runat="server"></asp:button>

btnCancel.Attributes.Add("oncl­ick", "vbscript: confirm()");