title: Meaning of JavaScript directive
body: <p>I saw this JavaScript code in some pages a few times:</p>
  
  <pre><code>&lt;script&gt;
        document.write('&lt;script src=js/vendor/'
          + ('__proto__' in {} ? 'zepto' : 'jquery')
          + '.js&gt;&lt;\/script&gt;');
      &lt;/script&gt;
  </code></pre>
  
  <p>I would like to know what exactly it does. I guess it serves to include jquery and zepto libraries.</p>