获取可见元素的子元素的值

html代码片段：

<tr>
    <td class="td1">图片分类</td>
    <td class="td2">
        <select class="c333 sel" name="type" id="type_p"><!--js通过此select选择下面的一个li显示，另一个隐藏-->
            <option value="1">轮播图</option>
            <option value="2">展示图</option>
        </select>
    </td>
</tr>
<li class="clearfix" id="li_0">
    <div class="gamedata-size fl">{$item.width}*{$item.height}</div>
    <div class="gamedata-upload fl" style="width:250px">
        <div>
            <div class="fieldset flash" id="fsUploadProgress0"></div>
            &nbsp;&nbsp;&nbsp;<span id="spanButtonPlaceHolder0"></span>
            <input type="hidden" name="pic_url0" id="imgurl0" value="">
            <input type="hidden" name="width0" value="{$item.width}">
            <input type="hidden" name="height0" value="{$item.height}">
            <input type="hidden" name="extension0" value="{$item.extension}">
            <input type="hidden" name="info0" value="{$item.info}">
            <input type="hidden" name="key_select" value="0">
            <div class="gamedata2-modi" id="img0"></div>
        </div>
        <p class="error"></p>
    </div>
    <div class="gamedata-box fl">
        <h4 class="gamedata2-h4-title">示例要求</h4>
        <dl class="gamedata2-dl">
            <dt>
                <img src="{$item.src}" height="{$item.height}" width="{$item.width}" >
            </dt>
            <dd>
                <p class="gamedata2-img-txt clearfix">
                    <span class="gamedata2-img-txt-left fl">图片格式：</span>
                    <span class="gamedata2-img-txt-right fl">{$item.extension}</span>
                </p>
                <p class="gamedata2-img-txt h96">
                    <span class="gamedata2-img-txt-left fl">构图要求：</span>
                    <span class="gamedata2-img-txt-right fl">{$item.info}</span>
                </p>
            </dd>
        </dl>
    </div>
</li> 
<li class="clearfix" id="li_1" style="display: none;">
    <div class="gamedata-size fl">{$item.width}*{$item.height}</div>
    <div class="gamedata-upload fl" style="width:250px">
        <div>
            <div class="fieldset flash" id="fsUploadProgress1"></div>
            &nbsp;&nbsp;&nbsp;<span id="spanButtonPlaceHolder1"></span>
            <input type="hidden" name="pic_url1" id="imgurl1" value="">
            <input type="hidden" name="width1" value="{$item.width}">
            <input type="hidden" name="height1" value="{$item.height}">
            <input type="hidden" name="extension1" value="{$item.extension}">
            <input type="hidden" name="info1" value="{$item.info}">
            <div class="gamedata2-modi" id="img1"></div>
        </div>
        <p class="error"></p>
    </div>
    <div class="gamedata-box fl">
        <h4 class="gamedata2-h4-title">示例要求</h4>
        <dl class="gamedata2-dl">
            <dt>
                <img src="{$item.src}" height="{$item.height}" width="{$item.width}" >
            </dt>
            <dd>
                <p class="gamedata2-img-txt clearfix">
                    <span class="gamedata2-img-txt-left fl">图片格式：</span>
                    <span class="gamedata2-img-txt-right fl">{$item.extension}</span>
                </p>
                <p class="gamedata2-img-txt h96">
                    <span class="gamedata2-img-txt-left fl">构图要求：</span>
                    <span class="gamedata2-img-txt-right fl">{$item.info}</span>
                </p>
            </dd>
        </dl>
    </div>
</li>

js代码片段：

<script type="text/javascript">
    $("#type_p").change(function(){
        var v = $("#type_p").val();
        if(v == 1){
            $("#li_0").show();
            $("#li_1").hide();
        }else if(v == 2){
            $("#li_0").hide();
            $("#li_1").show();
        }
     }); 
    /*查找可见元素的子元素*/
    var key = $("li:visible").find("input[name=‘key_select‘]").val();//重点在这里： li:visible

    //操作var

</script>