求正确的radio个数算法！为什么算radio个数是1的时候，出错：underfined
当radio个数是1，下列算法会出错：underfined
求正确的radio个数算法
<script>function cnt() { //var radioCount = document.all.item("pay_class").length; var radioCount = document.baseinfo.pay_class.length; alert("radioCount: " + radioCount);}</script></head><body><form name="baseinfo" id="baseinfo" method="post"> <input type="radio" name="pay_class" id="pay_class" onclick="cnt()">MyRadio<br/> </form></body>function cnt() { var radioCount = document.getElementsByName("pay_class").length; alert("radioCount: " + radioCount);}