Chrome扩展程序在浏览器关闭之前执行某些操作

Question

Is there any way I can detect the whole browser closing and then calling a function just before it closes? This is for Google Chrome specifically. Essentially I need an alert for the user before it closes. This is going to be for a chrome extension.

I have tried

window.onbeforeunload = function() {
     alert("can't exit yet");
     return null;
}

and

window.addEventListener("beforeunload", function (e) {
  alert("can't exit yet");
  return null;
});

They both do nothing. Chrome still exits and doesn't alert.

Thanks so much for the help!

Answer 1

Based on the documentation of on the onbeforeunload event handler :

When this event returns a non-void value, the user is prompted to confirm the page unload.

and

Since 25 May 2011, the HTML5 specification states that calls to window.alert() , window.confirm() , and window.prompt() methods may be ignored during this event.

Answer 2

In the HTML5 specification states that calls to window.alert(), window.confirm(), and window.prompt() methods may be ignored during this event. However, some browsers may display your message in alert box if you return the string on callback:

window.onbeforeunload=function(){
    return "This is message before unload!";
}

while other display generic browser message;