javascript 焦点的两个问题_表单特效

<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]