var focused = true;

// Set the name of the hidden property and the change event for visibility
var hidden, visibilityChange;
if (typeof document.hidden !== "undefined") { // Opera 12.10 and Firefox 18 and later support
  hidden = "hidden";
  visibilityChange = "visibilitychange";
} else if (typeof document.mozHidden !== "undefined") {
  hidden = "mozHidden";
  visibilityChange = "mozvisibilitychange";
} else if (typeof document.msHidden !== "undefined") {
  hidden = "msHidden";
  visibilityChange = "msvisibilitychange";
} else if (typeof document.webkitHidden !== "undefined") {
  hidden = "webkitHidden";
  visibilityChange = "webkitvisibilitychange";
}

function handleVisibilityChange() {
    if (document[hidden]) {
        focused = false;
    } else {
        focused = true;
    }
}

if (typeof document.addEventListener === "undefined" ||
    typeof hidden === "undefined") {
    alert("This demo requires a browser, such as Google Chrome or Firefox, that supports the Page Visibility API.");
} else {
    // Handle page visibility change
    document.addEventListener(visibilityChange, handleVisibilityChange, false);
}


var leave_message = "Please be aware, you are about to be redirected to another location!";
function goodbye(e)
{
    if(!window.top.document.hasFocus() && !focused)
    {
        if(!e) { e = window.event; }
        //e.cancelBubble is supported by IE - this will kill the bubbling process.
        e.cancelBubble = true;
        e.returnValue = leave_message;
        //e.stopPropagation works in Firefox.
        if (e.stopPropagation)
        {
            e.stopPropagation();
            e.preventDefault();
        }

        //return works for Chrome and Safari
        return leave_message;
    }
}

window.onbeforeunload=goodbye;