How can I make a JavaScript alert before a page closes?

I want to write JavaScript code that would, when开发者_如何学Go I close the current HTML page, display an alert message like "Are you sure?"

I want to take the value of the button from the alert message, whatever the user pressed. How can I do this?

You can use window.onbeforeunload

As far as I know, beforeunload is never fired in Opera.

For supporting that browser, you probably have to build some page-leaving-detection engine yourself (observing links etc).

You could do:

function close_window() {
  if (confirm("Close Window?")) {
    close();
  }
}

Check out this post: How to close current tab in a browser window?

$(document).ready(function(){
    $(window).bind("beforeunload", function(e) {
            return "alert message";
    });
});