Javascript: Call URL before Exit from Page

gistfile1.txt

window.onbeforeunload = function() {
   var URL = '//preview.adskom.net/test12345.js';
   var request = null;

    if (window.XMLHttpRequest){
        request = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        request = new ActiveXObject("Microsoft.XMLHTTP");
    }

    if (request) {
        request.open("GET", URL, true);
        request.send();
    }
}