Load JS scripts asynchronously w/ callback

loadScript.js

function loadScript(src, callback) {
    var s = document.createElement("script"),
        onEvent = ('onreadystatechange' in s) ? 'onreadystatechange' : 'onload';
    s[onEvent] = function () {
        if (("loaded,complete").indexOf(this.readyState || "loaded") > -1) {
            s[onEvent] = null;
            if (callback) {
                callback();
            }
            s.parentNode.removeChild(s);
        }
    };
    s.src = src;
    document.body.appendChild(s);
}