javascript如何显示和隐藏table中以某某字符开头的行 & 计算 tr和td的个数？

Question

<script defer>
function showt1(){
var oo = document.getElementsByTagName("TR");
var k=0
for(var i=0,j=oo.length;i<j;i++){if(oo[i].id.indexOf("tr1")>-1){oo[i].style.display="";k++;}}
alert(k);
}
function getnum(){alert("tr:"+document.getElementsByTagName("TR").length+"\ntd:"+document.getElementsByTagName("TD").length);}
</script>
<input type="button" value="显示t1" onclick="showt1()"/>
<input type="button" value="计算tr,td" onclick="getnum()"/>
<table id="table1" style="width: 100%;"> 
            <tr id="tr1"> 
                <td> 
                    第1 行：tr1 
                </td> 
            </tr> 
            <tr id="tr11" style="display:none "> 
                <td> 
                  &nbsp;&nbsp;&nbsp; 
                  第2 行：tr11 
                </td> 
            </tr> 
            <tr id="tr111" style="display:none "> 
                <td> 
                  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
                  第3 行：tr111 
                </td> 
            </tr> 
            <tr id="tr1111" style="display:none "> 
                <td> 
                  &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
                  第4 行：tr1111 
                </td> 
            </tr> 
            <tr id="tr21" style="display:none "> 
                <td> 
                    &nbsp;&nbsp;&nbsp; 
                    第5 行：tr21 
                </td> 
            </tr> 
            <tr id="tr211" style="display:none "> 
                <td> 
                    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
                    第6 行：tr211 
                </td> 
            </tr> 
        </table>