用JS判断单选按钮是否选中

<script>function check(){var flag = false;if(form1.info_type != null){    var msglen=form1.info_type.length;    for(i=0;i<msglen;i++){      if(form1.info_type[i].checked==true){        flag = true;      }    }}if (flag == false){    alert("对不起，请选择")    return false;}}</script><form id="form1" name="form1" method="post" action="" onsubmit="return check();"><td height=30>A   <input type="radio" name="info_type" value="A">   B   <input type="radio" name="info_type" value="B">   C   <input type="radio" name="info_type" value="C">   <label>   <input type="submit" name="Submit" value="提交" />   </label></td></form>

 

大家自己看下把 很好理解的 希望对大家有用