Javascript Async Example
<script>
(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('http://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'));
</script>