如何取table中td的id号为何td赋值？

Question

    <table>
                <tr>
                   <td id="1_1" align="center"> </td>                                                        </tr>
         </table>

Answer 1

  document.getElementById("1_1").innerHTML=""

Answer 2

document.getElementById("1_1").innerHTML="你要给的值"

Answer 3

<td id="1_1" align="center"> </td>document.getElementById("1_1").innerHTML="哈哈"td就变为了<td id="1_1" align="center"> 哈哈</td>  是这个意思么？