判断radio是否选择

//判断radio是否选择
    if(form.departmentid.length){
     for(var i=0; i<form.departmentid.length; i++){
      if(form.departmentid[i].checked){
       return true;
      }
     }
     alert("请选择radio");
     return false;
    }else{
     if(form.departmentid.checked){
      return true;
     }else{
      alert("请选择radio");
      return false;
     }
    }