gistfile1.js

function load(url) {
  var scripts = document.getElementsByTagName('script')[0]
  var script = document.createElement('script');
  script.async = true;
  script.src = url;
  scripts.parentNode.insertBefore(script, scripts);
}
load('//apis.google.com/js/plusone.js');
load('//platform.twitter.com/widgets.js');
load('//s.widgetsite.com/widget.js');