XMLHttpRequest injection load javascript script.

XMLHttpRequest.js

//Before </body> tag
<script>
        var xhr = new XMLHttpRequest();
        xhr.open("get", "cookbook.js", true);
        xhr.onreadystatechange = function () {
            if (xhr.readyState == 4) {
                if (xhr.status >= 200 && xhr.status < 300 || xhr.status == 304) {
                    var script = document.createElement("script");
                    script.type = "text/javascript";
                    script.text = xhr.responseText;
                    document.body.appendChild(script);
                }
            }
        };
        xhr.send(null);
</script>