js判断checkbox是否选中个数的方法(超简单)

<SCRIPT LANGUAGE="JavaScript">	//判断同类型	function checkboxnum(){	 var form = document.forms['formbj1'];	 var i,j=0;	 for (i=0; i<form.length; i++){	 var e=form[i];	 if (e.checked && e.type=='checkbox' && e.name=='bjid[]') {	  j++;	  if(j==3){		alert("最多只能选择2项！");		return false;		break;	  }	 }	 }	}	</script><form action="zhdk_bj.php" method="post" name="formbj1" id="formbj1"><input name="bjid[]" id="bjid[]" type="checkbox" onclick="return checkboxnum()" value="1" /><input name="bjid[]" id="bjid[]" type="checkbox" onclick="return checkboxnum()" value="2" /><input name="bjid[]" id="bjid[]" type="checkbox" onclick="return checkboxnum()" value="3" /></form>