<script>

function show()

{

    var a2=document.getElementById("div2");

    if(a2.style.display=="block")

    {

        a2.style.display="none";

        }

    else

    {

        a2.style.display="block";

    }

}

</script>

<input  type="button"  value="显示/隐藏"  onclick="show()"/>

<div id="div2">你好啊</div>