How do you prevent javascript page from navigating away?

Question

How do you prevent javascript page from navigating away?

Answer 1

Use onunload.

For jQuery, I think this works like so:

$(window).unload(function() { 
  alert("Unloading"); 
  return falseIfYouWantToButBeCareful();
});

Answer 2

In Ayman's example by returning false you prevent the browser window/tab from closing.

window.onunload = function () {
  alert('You are trying to leave.');
  return false;
}

Answer 3

Using onunload only allows you to display messages, but it will not interrupt the navigation (because it is too late). However, you can use onbeforeunload and it will interrupt navigation:

window.onbeforeunload() {
  return "Are you sure you want to navigate away?";
}

EDIT: Removed confirm() in return statement as this caused a confirm window as expected, but also showed a second confirm with the result of the first confirm.