Someone

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

return false
}
</script>

<a href="#foobar" onclick="return showHide('howitworks');">Link</a>