[résolu] Menu avec javascript non intrusif simplifié

function showmenu() {
if (!document.getElementsByTagName) return false;
var dls = document.getElementsByTagName("dl");
for (var a=0;a<dls.length;a++) {
  var dds = dls[a].getElementsByTagName("dd");
  for (var b=0;b<dds.length;b++) {
      dds[b].style.display='none';
      if (dds[b].previousSibling.tagName == "dt"){
        dds[b].previousSibling.addEventListener('click', function() {dds[b].style.display='block';}, false);
      }
    }
  }
}
window.onload=showmenu;

<dl id="menu">

		<dt><a href="#">Menu 1</a></dt>
			
		<dt >Menu 2</dt>
			<dd>
				<ul>
					<li><a href="#">Sous-Menu 2.1</a></li>
					<li><a href="#">Sous-Menu 2.2</a></li>

					<li><a href="#">Sous-Menu 2.3</a></li>
				</ul>
			</dd>	

		<dt>Menu 3</dt>
			<dd>
				<ul>
					<li><a href="#">Sous-Menu 3.1</a></li>
					<li><a href="#">Sous-Menu 3.1</a></li>

					<li><a href="#">Sous-Menu 3.1</a></li>
					<li><a href="#">Sous-Menu 3.1</a></li>
					<li><a href="#">Sous-Menu 3.1</a></li>
					<li><a href="#">Sous-Menu 3.1</a></li>
				</ul>
			</dd>
  <dt>Menu 4</dt>
			<dd>
				<ul>
					<li><a href="#">Sous-Menu 4.1</a></li>
					<li><a href="#">Sous-Menu 4.1</a></li>
				</ul>
			</dd>

	
</dl>

var alsa =
{
	addLoadEvent: function(func)
	{
		var oldonload = window.onload;
		if( typeof window.onload != 'function' )
		{
			window.onload = func;
		}
		else
		{
			window.onload = function()
			{
				oldonload();
				func();
			}
		}
	},
	display: function()
	{
		if( !document.getElementById || !document.getElementsByTagName ) return false;
		var oDl = document.getElementById('menu').getElementsByTagName('dl'),
			oList = document.getElementById('menu').getElementsByTagName('dd'),
			iI = oDl.length - 1,
			iJ = oList.length - 1;
		for( iJ; iJ>=0; iJ-- )
		{
			oList[iJ].style.display = 'none';
		}
		for( iI; iI>=0; iI-- )
		{
			if( oDl[iI].getElementsByTagName('dd')[0] )
			{
				oDl[iI].onmouseover = function()
				{
					this.getElementsByTagName('dd')[0].style.display = 'block';
				}
				oDl[iI].onmouseout = function()
				{
					this.getElementsByTagName('dd')[0].style.display = 'none';
				}
			}
		}
		return true;
	}
};
alsa.addLoadEvent(alsa.display);