Tiny script loader thing

loadScript.js

function loadScript(url, callback) {
    var script = document.createElement('script');
    var entry = document.getElementsByTagName('script')[0];
    var readyHandler;
    script.async = true;
    script.src   = url;
    entry.parentNode.insertBefore(script, entry);

    if (script.addEventListener) {
        script.addEventListener('load', callback, false);
    } else {
        script.attachEvent('onreadystatechange', readyHandler = function() {
            if (/complete|loaded/.test(script.readyState)) {
                callback();
                script.detachEvent('onreadystatechange', readyHandler);
            }
        });
    }
}