How I can allow user's browser to actually leave page once beforeunload event is fired?

As I ask upon stackoverflow:
https://stackoverflow.com/q/67535677/4706711

I want once user confirms that wantr to leave a page to actually leave. The code so far is:

                    window.beforeunload = function(e){
                        var confirmAction = confirm("Wanna leave? This will BREAK the page.");
                        if(confirmAction){
                            //leavePage
                        }
                    };

But I do not know how I can allow user to leave once user accepts. Do you have any idea why?

Comments

[Nico Zerpa (he/him)]

The beforeunload event is quite special due to security reasons. You can't launch a confirm inside this event, but there's a way to prompt the user if they want to leave, this is the code:

window.onbeforeunload = function(event) {
  event.preventDefault();
  event.returnValue = '';
}

This will make the browser ask the user if they really want to leave the page, and will unload the page if the user says Yes.