Load javascript file dynamically and call a function from it

script.js

(function (d, f, a) {
    // Your settings here
    var o = {
        maxLinks: 4,
        searchElements: ['div', 'h'],
        linkClass: 'link-to-mdn',
        extraLinks: {
            'keywordx': 'http://example.com'
        }
    };

    var s = d.createElement("script");
    s.type = "text/javascript";
    if (s.f) {
        s.a = function () {
            if (s.f == "loaded" || s.f == "complete") {
                s.a = null;
                PromoteMDN(o)
            }
        }
    } else {
        s.onload = function () {
            PromoteMDN(o)
        }
    }
    s.src = "promote-mdn.js";
    d.getElementsByTagName("head")[0].appendChild(s)
})(document, 'readyState', 'onreadystatechange');