急急急！！各位大神帮忙看一下这个js

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'contract .jsp' starting page</title>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<!--<link rel="stylesheet" type="text/css" href="styles.css">-->
</head>
<body bgcolor="#EAEAEA">
   <form action="" method="post" name="form1">
<table>
  <tr>
    <td>
     <div id="11" style="position: absolute;">
<input type="text" size="15" name="in1" value="请输入/选择">
    </div>
    <div id="12" style="position: absolute; visibility: hidden;">
      <select name="s1"onBlur="12.style.visibility='hidden';11.style.visibility='visible';13.style.visibility='visible'">
<option value="111">请选择</option>
<option value="222">123</option>
<option value="333">456</option>
     </select>
   </div>
           <div id="13" style="position: absolute; left: 126; top: 19">
    <select
name="s2"onMousedown="12.style.visibility='visible';11.style.visibility='hidden';13.style.visibilit='hidden'">
    </select>
 </div>
      </td>
   </tr>
</table>
      </form>
    </body>
</html>
主要实现：下拉框既可以下拉选择，又可以填写内容。
  div id="13" style="position: absolute; left: 126; top: 19"></div>中的onMousedown事件无法触动。求详解！！