<script>

    $(document).ready(function(){
        $.getJSON("getlist.php", function(return_data){

            return_data.forEach(function(e,i){
                $('#catn').append('<option value= "'+e.catname+'">'+e.catname+'</option>');
            });

        });
    });

    $(document).ready(function(){
        $.getJSON("list2.php",{'catname':catname},function(return_data){

            return_data.forEach(function(h,i){
                $('#scatn').append('<option value= "'+h.subcatname+'">'+h.subcatname+'</option>');
            });

        });
    });

<?php
 $catname=$_GET['catname'];
 $conn =mysqli_connect("localhost", "root", "", "project");

      $sql = "SELECT * FROM catd where catname='$catname'";
      $result = mysqli_query($conn, $sql);


$scat_arr = array();
 while( $row = mysqli_fetch_array($result) )
 {
    $catid = $row['cid'];
    $catname = $row['catname'];
    $scat_arr[] = array("cid" => $catid, "catname" => $catname);
}
echo json_encode($scat_arr);
 ?>