Suppose a user enters some information on the page and tries to close or navigate from the windowwithout saving the data. You may want to warn the user about possible data loss.
To do this, use the window DOM object's onbeforeunload event, which is fired just before the unload event. Its sole purpose is to allow users to change their minds about exiting the page. That is to say, it cancels the upcoming unload event. The code is below:
window.onbeforeunload = Func1
//statements to execute
return 'some message';
If you have set the onbeforeunload
handler, and later want to cancel the event handling, simply assign it a null
window.onbeforeunload = null;
to be a user-defined custom method of the window object. Perfectly acceptable.