function shou () { document.getElementsByTagName('div').style.display = "block"; } <button onclick="shou()"> Показать</button>
function show() { var elements = document.getElementsByTagName("DIV"); for(var i = 0, leng = elements.length; i < leng; i++) { elements[i].style.display = "block"; } }
<div style='display: none; width: 100px; height: 100px; background:red'></div> <button onclick='show()'> Показать</button> <script> function show() { document.getElementsByTagName('div')[0].style.display = "block"; return false; } </script>