Onbeforeunload not working on Chrome/Firefox but w

问题:

I wrote a code for onbeforeunload. It works for IE but not for any other browser.

var unloadFunction = function(){return "";}
window.addEventListener('beforeunload', unloadFunction); 

What can possibly go wrong with this code. :( I am not able to understand. I want this to work in all browsers in order to show a confirm popup to the user before one exist the page.

回答1:

Before unload processing has been modified since it was introduced due to badly behaved web pages. In result, browsers may or may not suppress alerts during unload event processing.

Refer to MDN for detailed information, but note the returnValue mentioned is a property of the event object, not a value returned from the event handler function.

The example below runs in major browsers and IE (for windows 10 at least).

• Firefox and IE reported the message provided in event.returnValue.
• Chrome ignored the message and simply asked

  Leave site?
  Changes that you made may not be saved.

• Only IE showed the alert box.

var unloadFunction = function( event){
    event.returnValue = "do you really want to leave this page";
    alert("unloading");
};
window.addEventListener('beforeunload', unloadFunction);