for (var i = 1; i <= 10; i++) {	
	if (eval("document.getElementById('menu_item"+i+"')")) {
		document.getElementById('menu_item'+i).onmouseover = function () {
			var ss = this.id.replace('menu_item', 'ss');
			document.getElementById(ss).style.visibility = 'visible';
		}
		
 		document.getElementById('menu_item'+i).onmouseout = function () {
			var ss = this.id.replace('menu_item', 'ss');
 			document.getElementById(ss).style.visibility = 'hidden';
 		}
	}
}