获取单选的值

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<scriptlanguage=javascript>
functionA()
{
for(vari=0;i<document.formname1.ST_CLASS.length;i++)
{
if(document.formname1.ST_CLASS[i].checked==true)
{
vara=document.formname1.ST_CLASS[i].value;
alert(a);
}
}
}
</script>