function toggleVis(obj)
{
var el = document.getElementById(obj);
if ( el.style.display != 'none' )
{
el.style.display = 'none';
}
else
{
el.style.display = '';
}
}
<div id="toggled">Hi there!!!
</div>
<a href="#" onclick="toggleVis( document.getElementById( 'toggled' ) ) ; return false">Toggle!
</a>