function addLoadEvent(func) {
	var oldonload=window.onload;
	if(typeof window.onload!='function') {
		window.onload=func;
	} else {
		window.onload=function() {
			oldonload();
			func();
		}
	}
}
//下拉菜单
function menuFix() { 
 var sfEls = document.getElementById("nava").getElementsByTagName("li");
for (var i=0; i<sfEls.length; i++) { 
sfEls[i].onmouseover=function() { 
this.className+=(this.className.length>0? " ": "") + "sfhover"; 
} 
sfEls[i].onMouseDown=function() { 
this.className+=(this.className.length>0? " ": "") + "sfhover"; 
} 
sfEls[i].onMouseUp=function() { 
this.className+=(this.className.length>0? " ": "") + "sfhover"; 
} 
sfEls[i].onmouseout=function() { 
this.className=this.className.replace(new RegExp("( ?|^)sfhover\\b"), 
""); 
} 

}
 
} 
addLoadEvent(menuFix);