做个onlick时间，使下拉框展开

比如：做个按钮，按钮上定义一个onlick事件，按钮后面紧接着是一个可供选择的下拉框；
现在效果这样：我点击按钮，能使按钮后面的下拉框自动展开。
也就是说在onlick事件中怎么定义才能使下拉框获得焦点而展开，查了好多资料，也没找着自己想要的，诸位有什么好的建议。

解决方案 »

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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>伸缩的菜单-/</title>
<style>

</style>
<script language="javascript">
function change(){
//通过父元素li，找到兄弟元素ul
var oSecondDiv = this.parentNode.getElementsByTagName("ul")[0];
//CSS交替更换来实现显、隐
if(oSecondDiv.className == "myHide")
oSecondDiv.className = "myShow";
else
oSecondDiv.className = "myHide";
}
window.onload = function(){
var oUl = document.getElementById("listUL");
var aLi = oUl.childNodes; //子元素
var oA;
for(var i=0;i<aLi.length;i++){
//如果子元素为li，且这个li有子菜单ul
if(aLi[i].tagName == "LI" && aLi[i].getElementsByTagName("ul").length){
oA = aLi[i].firstChild; //找到超链接
oA.onclick = change; //动态添加点击函数
}
}
}
</script>
</head>
<body>
<div id="navigation">
<ul id="listUL">
<li><a href="#">Home</a></li>
<li><a href="#">News</a>
         <ul class="myHide">
             <li><a href="#">Lastest News</a></li>
                <li><a href="#">All News</a></li>
            </ul>
        </li>
<li><a href="#">Sports</a>
         <ul class="myHide">
             <li><a href="/">Basketball</a></li>
                <li><a href="#">Football</a></li>
                <li><a href="#">Volleyball</a></li>
            </ul>
        </li>
<li><a href="#">Weather</a>
         <ul class="myHide">
             <li><a href="#">Today's Weather</a></li>
                <li><a href="#">Forecast</a></li>
            </ul>
        </li>
<li><a href="#">Contact Me</a></li>
</ul>
</div>
</body>
</html>你是说这种吗
<script language="javascript">
var showSelect= false;
document.onclick = hideItems;
function hideItems(){
   if(showSelect!=true){
    if(document.all.selectDiv!=null){
     document.all.selectDiv.style.visibility='hidden';
     if(document.all.selectid!=null){
      document.all.selectid.disabled=false;
     }
    }
   }
   showSelect = false;
}
function showPullDown(){
   if(document.all.selectDiv!=null){
    var selectObj = document.getElementById("selectid");
    if(selectObj!=null && selectObj.size==1){
     selectObj.size=2;
     selectObj.style.height=getPullDownHeight(selectObj.length);
     selectObj.style.width=172;
    }
    document.all.selectDiv.style.visibility='visible';
    showSelect = true;
   }
}
function getPullDownHeight(length){
   switch(length){
    case 0:
     return 0;
    case 1:
     return 30;
    case 2:
     return 50;
    case 3:
     return 60;
    case 4:
     return 80;
    default:
     return 100;

   }

}
</script>
<TABLE cellspacing="0" cellpadding="0" align="left">
      <TR>
        <TD nowrap="false">
    <input type="button" value="show pulldown below me"/>
    <input type="button" value="▼" onclick="showPullDown()" />
        </TD>
      </TR>
      <TR>
      <TD>
    <div id="selectDiv" style="padding-left:3px; position:absolute; z-index:1000;visibility:hidden">
       <select id="selectid" name="selectid" style="font-size:16px;font-weight: bold" size="1">
        <option selected value='2'>02月</option>
        <option value='9'>09月</option>
        <option value='10'>10月</option>
       </select>
    </div>
      </TD>
      </TR>
</TABLE>
不是：
<body>
    <input type="button" value="展开" onclick="showchange()">

    <select id="select" >
     <option>请选择</option>

     <option>select1</option>
     <option>select2</option>
     <option>select3</option>
     <option>select4</option>
    </select>
  </body>点击展开  按钮后面的下拉框自动展开，关键是 js showchange()的写法
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
  <title>无标题页</title>
<script src="http://hi.images.csdn.net/js/public/jquery-1.2.3.pack.js" type="text/javascript"></script></head>
<body>
<div style="position:relative; border:1px solid #ccc; width:100px" id="div">
点击显示
<ul style="display:none; position:absolute; left:0; top:5px; border:1px solid #666; width:100px">
<li>1111111111</li>
<li>11111111111</li>
<li>1111111111</li>
<li>11111111111</li>
<li>1111111111</li>
<li>11111111111</li>
<li>1111111111</li>
<li>11111111111</li>
<li>1111111111</li>
<li>11111111111</li>
</ul>
</div>
<script type="text/javascript">
document.getElementById("div").onclick = func;
function func(e)
{
e = window.event || e;
if(e.target.tagName=="DIV")
{
var list = e.target.getElementsByTagName("ul")[0];
var disp = list.style.display;
list.style.display=disp=="none"?"block":"none"
}
if(e.target.tagName == "LI")
{
  alert("你选择了:"+e.target.innerHTML)
}
}</script>
  </body>
</html>
document.onclick = hideItems;
这个去掉就好了把?
这里报 if(e.target.tagName=="DIV")
缺少对象的错误啊