using onbeforeunload event, url change on selecting stay on this page

Question

Rewriting the question -

I am trying to make a page on which if user leave the page (either to other link/website or closing window/tab) I want to show the on

Answer 1

After playing a while with this problem I did the following. It seems to work but it's not very reliable. The biggest issue is that the timed out function needs to bridge a large enough timespan for the browser to make a connection to the url in the link's href attribute.

jsfiddle to demonstrate. I used bing.com instead of google.com because of X-Frame-Options: SAMEORIGIN

var F = function(){}; // empty function
var offerUrl = 'http://bing.com';
var url;


var handler = function(e) {
    timeout = setTimeout(function () {
        console.log('location.assign');
        location.assign(offerUrl);

    /*
     * This value makes or breaks it.
     * You need enough time so the browser can make the connection to
     * the clicked links href else it will still redirect to the offer url.
     */
    }, 1400);

    // important!
    window.onbeforeunload = F;

    console.info('handler');
    return 'Do you wan\'t to leave now?';
};

window.onbeforeunload = handler;