Closing web tab

Question

I've seen this on a few websites, where when you close a tab and an important process is running it asks the client if they want really want to leave.

I would like to know if it's the web browser itself, or specific Javascript code.

If it is Javascript code, what code would it be? and where can I read more on it?

Answer 1

here's a snippet from Stackoverflow.com

window.onbeforeunload = function() { return "Hey, you're leaving the site. Bye!"; };

Answer 2

@Limitless its a confirm box (javascript code)
here is a snippet copied from the javascript course:-

var result = confirm("Do you really want to leave this page?");
if (result == true) {
alert("Thanks for visiting");
}
else {
alert("Thanks for staying with us");
}

Answer 3

So how do we determine if the user is trying to close the tab?

Answer 4

@empty check the course !!!