Optimised async loading of cross-domain scripts

snippet.js

/*
 * 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.
 * Tip: http://pivotallabs.com/users/jdean/blog/articles/1400-working-with-asynchronously-loaded-javascript
 */

(function(doc, script) {
    var js, 
        fjs = doc.getElementsByTagName(script)[0],
        add = function(url, id) {
            if (doc.getElementById(id)) {return;}
            js = doc.createElement(script);
            js.src = url;
            id && (js.id = id);
            fjs.parentNode.insertBefore(js, fjs);
        };

    // Google Analytics
    add(('https:' == location.protocol ? '//ssl' : '//www') + '.google-analytics.com/ga.js', 'ga');
    // Google+ button
    add('https://apis.google.com/js/plusone.js');
    // Facebook SDK
    add('//connect.facebook.net/en_US/all.js', 'facebook-jssdk');
    // Twitter SDK
    add('//platform.twitter.com/widgets.js', 'twitter-wjs');
}(document, 'script'));

snippet_onload.js

/*
 * Updated to use the function-based method described in 
 * http://www.aaronpeters.nl/blog/why-loading-third-party-scripts-async-is-not-good-enough
 *
 * N.B. Be sure to include Google Analytics's _gaq and Facebook's fbAsyncInit prior to this function.
 * Tip: http://pivotallabs.com/users/jdean/blog/articles/1400-working-with-asynchronously-loaded-javascript
 */
<script>
(function(w, d, s) {
  function go(){
    var js, fjs = d.getElementsByTagName(s)[0], 
        add = function(url, id) {
	  if (d.getElementById(id)) {return;}
	  js = d.createElement(s); js.src = url; id && (js.id = id);
	  fjs.parentNode.insertBefore(js, fjs);
	};
    // Google Analytics
    add(('https:' == location.protocol ? '//ssl' : '//www') + '.google-analytics.com/ga.js', 'ga');
    // Google+ button
    add('https://apis.google.com/js/plusone.js');
    // Facebook SDK
    add('//connect.facebook.net/en_US/all.js', 'facebook-jssdk');
    // Twitter SDK
    add('//platform.twitter.com/widgets.js', 'twitter-wjs');
  }
  if (w.addEventListener) { w.addEventListener("load", go, false); }
  else if (w.attachEvent) { w.attachEvent("onload",go); }
}(window, document, 'script'));
</script>