</div>
  <button>Start</button>
  <script>
    (function() {
      var button = document.querySelector("button");
      button.addEventListener("click", function(evt) {
        var test1 = document.querySelector("#test1"),
            test2 = document.querySelector("#test2");
        test1.setAttribute("style", "width: 300px");
        test2.setAttribute("style", "width: 300px");
      }, false);
    })();
  </script>
</body>
