When I edit a page and try to leave it I get a dialog box that appears and asks me if I want to:
Leave this Page or Stay on this Page
The dialog blocks me from doing anything until I have answered.
In Javascript the only similar thing I see is window.confirm(message) which gives and OK and Cancel button.
So is there another way in Javascript that I can create a dialog that I don't know about? Please note that I want to create a dialog at any time and I am not interested in knowing when the page closes so this is not a duplicate of the question identified by Zeta.