Giving unique ID to the dropdown and use it for response

Question

I have a purchase bill form which i add row by javascript and retrieve values from mysql database by php.

function addRow(dataTable) {
var table = document.getElementById("dataTable");

var rowCount = table.rows.length;
if(rowCount < 100) {
    var row = table.insertRow(rowCount);
    var colCount = table.rows[0].cells.length;
    for(var i=0; i<colCount; i++) {
        var newcell = row.insertCell(i);
      newcell.innerHTML = table.rows[0].cells[i].innerHTML;
      }  

    table.appendChild(newrow);   
 } else {
    alert("En fazla 100 satır ekleyebilirsiniz.");
}
var selects = newrow.getElementsByTagName('select'); 
    for(var i=1; i<selects.length;i++) {
        selects[i].id = Math.random().toString(36).slice(2); 
    }
    }
 function fetch_select(val) {
 $.ajax({
    type: 'post',
    url: 'stoklari_cek.php',
    data: {sto_altgrup_kod:val},
    success: function (response) {
        document.getElementById("kodlar").innerHTML=response; 
    }
});
}

In the first row when i change first select value i can get the second secelt values from database. But when i add new row and change the first select value, it changes the first rows second select. I tried to give unique ID for each select elements with this code but i could not call it back on the second part of codes. Shortly i want to change second select option values when i change the first select value in each row i added.

This is first select element of every row.

<select style="margin: 0 !important; padding: 0 !important; width:100%" name="gruplar" id="gruplar"  class="gruplar" onChange="fetch_select(this.value)" required>
    <option value="">--Alt Gruplar--</option>
<?php $altgrup_al = mysql_query("SELECT * FROM stok_alt_gruplari ORDER BY sta_isim ASC");
while($altgrup_cek = mysql_fetch_array($altgrup_al)){
$sta_isim = $altgrup_cek['sta_isim'];
$sta_RECno = $altgrup_cek['sta_RECno'];
echo '<option ';
echo 'value="'.$altgrup_cek['sta_RECno'].'">'.$altgrup_cek['sta_isim'].'</option>';}?>
</select>

And this is the second select that values should change according to the first select above.

<select style="margin: 0 !important; padding: 0 !important; width:100%"     class="kodlar" id="kodlar"  name="sth_stok_kod[]" required>
<option value="">--Ürünler--</option>