showFollowButton = function() {
      var tagName = 'script',
          id = 'twitter-wjs',
          fjs = document.getElementsByTagName(tagName)[0],
          protocol = /^http:/.test(document.location) ? 'http' : 'https';

      if (!document.getElementById(id)) {
        var js = document.createElement(tagName);
        js.id = id;
        js.src = protocol + '://platform.twitter.com/widgets.js';
        fjs.parentNode.insertBefore(js, fjs);
      } else {
        // The twitter script was loaded already.
        window.twttr.widgets.load();
      }
    }
Twitter button. Copy pasted from:
https://about.twitter.com/resources/buttons#follow