Table with inputs, sum minus operations

by Akram kamal

HTML

<table>
    <thead>
        <tr>
            <th>Qty1</th>
            <th>Qty2</th>
            <th>Qty3</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td>
                <input type="text" id="noCajas1_1" class="noCajas" value="5" size="7" readonly="readonly" />
            </td>
            <td>
                <input type="text" id="noCajas1_2" class="noCajas" value="0" size="7" />
            </td>
            <td>
                <input type="text" id="noCajas1_3" class="noCajas" value="5" size="7" readonly="readonly" />
            </td>
        </tr>
        <tr>
            <td>
                <input type="text" id="noCajas2_1" class="noCajas" value="9" size="7" readonly="readonly" />
            </td>
            <td>
                <input type="text" id="noCajas2_2" class="noCajas" value="0" size="7" />
            </td>
            <td>
                <input type="text" id="noCajas2_3" class="noCajas" value="9" size="7" readonly="readonly" />
            </td>
        </tr>
    </tbody>
</table>

JavaScript

$('.noCajas').on('keyup', function () {
    var $inputs = $(this).parents('tr').find("input");
    var answer = $inputs.eq(0).val() - $inputs.eq(1).val();
    if (Number.isNaN(answer)) 
        $inputs.eq(2).val("err")
    else 
        $inputs.eq(2).val(answer)
})