我想单击位于表中特定行的按钮，并将数据显示在表的特定单元格中

This is what I tried to do but I can't get it to work, can anyone help me. I would like to click on the approve button and get value of input with name="documentno" of the same row as the button I clicked on. Thank you

<form class="form-inline" action="approval.php" method="post"enctype="multipart/form-data">
<table class="table table-hover"  id="detailTable">
                     <thead>
                        <tr>
                         <th>Document no</th>
                         <th>Code</th>
                         <th>Name</th>
                         <th>Approve</th>
                         <th>Reject</th>
                           </tr>
                    </thead>
                      <tbody>
                        <tr id="somerow">
                       <?php
                       if($select==""){

                         while($rowstep34id = mysqli_fetch_array($querystep34)){
                          //echo "<td>" . $rowstep3['itemcode'] . "</td><td>" . $rowstep3['itemdescription'] . "</td><td>" . $rowstep3['quantity'] . "</td><td>" . $rowstep3['unitprice'] . "</td><td>" . $rowstep3['total'] . "</td><td>" . $rowstep3['remarks'] . "</td></tr>";
                          echo "<td><input type='text'  name='documentno' value='" . $rowstep34id['id'] . "'   readonly /></td>
                                <td><input type='text'  name='vendorcode' value='" . $rowstep34id['code'] . "'  readonly /></td>
                                <td><input type='text'  name='vendorname' value='" . $rowstep34id['name'] . "'  readonly /></td>

                                <td><button type='button' class='btn btn-primary' name='approve' onclick='tgPanel(this)'>approve</button></td>
                                <td><button type='button' class='btn btn-primary' name='reject'>reject</button></td>
                                </tr>";     
                        }
                         }
                        ?> 
                        </tbody>
                      </table>
                      </form>

<script>
function tgPanel(button) {
     var tr = button.parentElement.parentElement;
    var Row = document.getElementById("somerow");
var Cells = Row.getElementsByTagName("td");
alert(Cells[0].innerText);  
}
</script>

If you could define some id or data-id to your rows it would be possible to do smth like that:

$(#row-id button).on("click", function{tgPanel($(this)});

function tgPanel(button)
{
    var data= button.closest("input[name='documentno']").val();
}

With your current markup you can get the value of documentno input from the same row by the following.

function tgPanel(button) {

  let documntnoVal = button.closest('tr').querySelector('input[name="documntno"]').value; 

  //remaining code ....
}

//The idea is when you click the approved button just select the parent tr (which will be the row containing approved button that is just clicked) and then select the input with name="documntno" which is your desired element.

NOTE: In your markup it seems you missed an opening "< tr >" tag in echo, so please make sure your markup is valid.