javascript 焦点的两个问题

<meta http-equiv="Content-Type" content="text/html;charset=UTF-8"> <title>无标题页</title> <input name="r0" id="r0" type="text" size="3" maxlength="1" onkeydown="key_down(id)"><input name="r1" id="r1" type="text" size="3" maxlength="1" onkeydown="key_down(id)"><input name="r2" id="r2" type="text" size="3" maxlength="1" onkeydown="key_down(id)"><input name="r3" id="r3" type="text" size="3" maxlength="1" onkeydown="key_down(id)">
[ctrl+a 全选 注:如需引入外部js需刷新才能执行]