Js给表格每行动态添加input标签

代码片段:
head 标签中

  <script src="jquery-easyui-1.4.5/jquery.min.js">script>
<script type="text/javascript">
        function InserTab() {
            var trLen = $("#tab1 tr").length;
            var rowT = "" +
                "" +
                "" +
                "";
            var trPre = $("#tab1 tr:eq(" + (trLen - 1) + ")");
            $(rowT).insertAfter($(trPre));
        }
    script>

body标签中

<table id="tab1" style="width: 50%;">
        <tr>
            <td>列一td>
            <td>列二td>
            <td>列三td>
            <td>列四td>
        tr>
    table>

    <input type="button" value="添加" onclick="InserTab()" />