le display:none
     function toggleDisplay() {
       var els = document.getElementsByTagName('div'),
           el,
           cssVal;

       for (var i=0; i<els.length; i++) {
         el = els[i];
         cssVal = getComputedStyle(el, null).getPropertyValue('display');

         // toggle
         if (cssVal == 'none') el.style.display = 'block';
         else el.style.display = 'none';
       }
     }
    </script>
  </head>
  <body>
    <button onclick="addDiv();">Add more DIVs</button>
    <button 