i have

<table id="tbl_dtl">
<tr class = "table_print" id="sub_klp_row<?php echo $index;   ?>">
    <td id="sub_klp<?php echo $index;   ?>" class = "style6" ><?php echo    isset($sub_klp) ? $sub_klp : 'SUB KLP'   ?> </td>
</tr>
<table>

because i need to use if condition i want to add <td> code on below using javascript

    <td id="sub_klp<?php echo $index;   ?>" class = "style6" ><?php echo    isset($sub_klp) ? $sub_klp : 'SUB KLP'   ?> </td>

what i Already did so far

 if (current_sub_klp.trim() != previous_sub_klp.trim()) {
    //console.log(current_sub_klp); 
    var row = document.getElementsByClassName("sub_klp_row<?php echo $index; ?>");
    var td = document.createElement("td");
    td.name = "sub_klp<?php echo $index; ?>";
    td.id = "sub_klp<?php echo $index; ?>";
    row.appendChild(td);
}