checkBox 验证 不超过固定项

function addEventHandler(oTarget, sEventType, fnHandler) {
if (oTarget.addEventListener) {
   oTarget.addEventListener(sEventType, fnHandler, false);//firefox
} else if (oTarget.attachEvent) {
   oTarget.attachEvent("on" + sEventType, fnHandler);//ie
} else {
   oTarget["on" + sEventType] = fnHandler;//other
}
}
 

var elems=document.getElementsByName("q14");
var MAX_CHECKED_COUNT=2;
var countClick=0;



var getCheckCount=function(nameStr)
{
     var elems = document.getElementsByName(nameStr);
        var num = 0;
        for (var i = 0; i < elems.length; i++) {
            if (elems[i].checked)
            { num++; }
		}	
			return num;
}
//
//var clickHandler=function(e){
// var getNum=getCheckCount("q14");
// //alert(getNum)
// if(getNum<=2)
// {
//	//if(!this.checked==true)
// }
// else
// {
// this.checked=false;
//   return false;
// }
//}

var clickHandler=function(e)
{ 
  var e=window.event||e;
  var elem=e.srcElement||e.target;
  countClick+=(elem.checked)?1: -1;
 // alert(countClick);
  if(countClick>MAX_CHECKED_COUNT)
  {
    elem.checked=false;
	countClick--;
	return false;
  }
  
 
}

for(var i=0,len=elems.length;i<len;i++)
{
 	addEventHandler(elems[i],"click",clickHandler)
}