[tsigel]

<style>.qwer {display: none}</style>
<div class="qwer">1</div>
<div class="qwer">2</div>
<div class="qwer">3</div>
<div class="qwer">4</div>
<div class="qwer">5</div>
<button onclick="show(); return false">показать</button>
<script>
document.querySelector(".qwer").style.display = "block";
function show() {
   var a =  document.querySelectorAll(".qwer");
   for (var i = 0; i < a.length; i++) {
      a[i].style.display = "block";
   }
}
</script>