how to style certain td in every 3rd table row?

Question

How to select every 4td in every 3rd row?

I have a jQgrid chart and id like to target the client column for every 3rd row starting with first one.

Here is an example: http://jsfiddle.net/ZHRaD/13/

Basic html:

<tr>
   <td></td>
   <td></td>
   <td></td>
   <td></td> // <<
   <td></td>
</tr>
<tr>
   <td></td>
   <td></td>
   <td></td>
   <td></td>
   <td></td>
</tr>
<tr>
   <td></td>
   <td></td>
   <td></td>
   <td></td>
   <td></td>
</tr>
<tr>
   <td></td>
   <td></td>
   <td></td>
   <td></td> // <<
   <td></td>
</tr>

....

Answer 1

You can use rows property of <table> DOM to access <tr> elements and cells property of <tr> to access <td> elements. The corresponding code can look like

loadComplete: function () {
    var rows = this.rows, cRows = rows.length, iRow, row,
        iSelRows = 0;
    for (iRow = 0; iRow < cRows; iRow++) {
        row = rows[iRow]; // row.id is the rowid
        if ($(row).hasClass("jqgrow")) {
            // the row is a standard row
            if (iSelRows%4 === 0) {
                $(row.cells[3]).addClass("ui-state-highlight");
            }
            iSelRows++;
        }
    }
}

The corresponding modified jsfiddle demo is here.