employeeTable.find(".command-edit").on("click", function(event)
  {
   var eid = $(this).data("row-id");

// At this point i can get the alert values o.k.

   alert("You pressed edit on row: " + $(this).data("row-id"));
   alert("You pressed edit on row: "+""+eid);

//but here is the issue

 $.ajax({
    url:"fetch_single.php",
    method:"POST",
    data:{eid:eid},
    dataType:"json",
    cache: false,

  success: function(data){
    alert('success');
  },

// its always failing.

  error: function(){
    alert('failure');
  }

<?php
//fetch_single.php

include_once("db_connect.php");

if(isset($_POST["eid"]))
{
 $output = array();

 $query = "SELECT * FROM employee WHERE id =      '".$_POST["eid       "]."'";
 $result = mysqli_query($connection, $query);
 while($row = mysqli_fetch_array($result))
 {
  $output["id"] = $row["id"];
  $output["employee_name"] = $row["employee_name"];
  $output["employee_salary"] = $row["employee_salary"];
  $output["employee_age"] = $row["employee_age"];

 }
 echo json_encode($output);
}

?>