Optimised async loading of cross-domain scripts with callback

async_callback.js

/*
 * Added callback
 *
 * Updated to use the function-based method described in http://www.phpied.com/social-button-bffs/
 * Better handling of scripts without supplied ids.
 *
 * N.B. Be sure to include Google Analytics's _gaq and Facebook's fbAsyncInit prior to this function.
 */

(function(doc, script) {
    var js, fjs = doc.getElementsByTagName(script)[0],
        getScript = function(url, id, callback) {
            if(doc.getElementById(id)) {return;} js = doc.createElement(script);
            js.src = url; id && (js.id = id); fjs.parentNode.insertBefore(js, fjs);
            js.onload = js.onreadystatechange = function() {
                if(!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete') {
                    if(callback) { callback(); }
                }
            };
        };
    getScript(('https:' == location.protocol ? '//ssl' : '//www') + '.google-analytics.com/ga.js', 'ga');
    getScript('//connect.facebook.net/en_US/all.js#xfbml=1', 'facebook-jssdk');
    getScript('//platform.twitter.com/widgets.js', 'twitter-wjs');
    getScript('//platform.linkedin.com/in.js?async=true', 'linkined-jsapi', function() { IN.init({ api_key: 'YOUR_API_KEY' }); });
}(document, 'script'));