focus() 方法用于赋予单选按钮焦点。
radioObject.focus()
下面的例子可为 "Male" 单选按钮设置焦点:
<html>
<body>
<form>
Male: <input id="male" type="radio" name="Sex" value="Male" />
<br />
Female: <input id="female" type="radio" name="Sex" value="Female" />
</form>
<script type="text/javascript">
document.getElementById('male').focus();
</script>
</body>
</html>