Access item inside div through javascript

Question

I have a div which contain other tags inside it

<div id="mainDiv">
    <div>
        <table>
            <tbody>
                   <tr>
                      <td>1</td>
                      <td>item</td>
                      <td>item</td>
                      <td>2</td>
                   </tr>
            </tbody>
        </table>
    </div>

    <div>
        <table>
            <tbody>
                   <tr>
                      <td>1</td>
                      <td>item</td>
                      <td>item</td>
                      <td>5</td>
                   </tr>
            </tbody>
        </table>
    </div>
</div>

How can I access <td> of this mainDiv through javascript. I want to change innerHTML of these <td>

Answer 1

var allDivTd = document.getElementById("mainDiv").getElementsByTagName("TD");

for(var i = 0; i < allDivTd.length; i++){
    var td = allDivTd[i];
    td.innerHTML = // do something w/ inner html
}