Count a th cell's place in table row

<table border="1">
    <tbody>
        <tr>
            <th>A</th>
            <th>B</th>
            <th>C</th>
        </tr>
        <tr>
            <td>aaa</td>
            <td>bbb</td>
            <td>ccc</td>
        </tr>
    </tbody>
</table>

How can I find out that the th cell with "B" is the second in the th row?

Test: http://jsfiddle.net/SNj27/1/

You could use eq() if it's always the second th element you want to target:

$('th:eq(1)').text(); // returns 'B'

Edit:

If it's not always the second element, you could use index() to determine whether it is in the second row or not.

if ($(this).text().trim() === "B") {
    console.log($(this).index()); 
    // Returns 1 and 2 respectively for your jsFiddle (0 index based) 
    // Meaning the first 'B' is in row 2, the second is in row 3.
}

jsFiddle.

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Note: You should use $.trim instead of trim(), as in IE8 and before, you will recieve a syntax error using trim():

if ($.trim($(this).text()) === "B")

jsFiddle.