js判断单选按钮简单代码

<form name="myform" action="" method="" onsubmit="return check()">
<input type="radio" name="picno" value="1">
<input type="radio" name="picno" value="2">
<input type="radio" name="picno" value="3">
<input type="submit" value="Submit">
</form>
<script language="JavaScript">
function check(){
    var flag=0
    for(i=0;i<myform.picno.length;i++)
    if(myform.picno[i].checked==true){ //检测单选按钮状态
        flag=1
        break
    }
    if(!flag){
        alert("请先选择更换图片的位置")
        return false
    }
}
</script>