JavaScript for Show & Hide Div...... Good Working

<script type="text/javascript">
    function showHide(id)
    {
        if(document.getElementById(id).style.display == "block")
        {
            document.getElementById(id).style.display = "none";
        }
        else
        {
            document.getElementById(id).style.display = "block";
        }
    }
</script>

Put this  code where you want to Show & Hide DIV.
<a href="#" onclick="showHide(1);">Portfolio</a>
            <div style="display:none;" id="1" class="menu_in"></div