How to keep form items selected after post request.Using onchange - php

Question

I have a problem when submit form value from the second select don't show. Can someone explain me what I'm doing wrong because in new in this (maybe is because i use onchange event). Thanks in advance.
index.php
<?php
include("includes/conn.php");
$sql = "SELECT * FROM opstina";
$result = $conn->query($sql);
if($result->num_rows > 0){
$opstineArr = array();
while($row = $result->fetch_assoc()){
$opstineArr[] = $row;
}
}
if(isset($_POST["addNesto"])){
$opstine = $_POST["opstine"];
$ime = $_POST["ime"];
if(isset($opstine)){
if(empty($opstine)){
$error["opstine"] = "izaberite opstinu";
}
}
$naselja = $_POST["naselja"];
if(isset($naselja)){
if(empty($naselja)){
$error["naselja"] = "izaberite naselje";
}
}
if(isset($ime)){
if(empty($ime)){
$error["ime"] = "izaberite ime";
}
}
if(count($error) == 0){
echo 2222;
}
}
include("includes/header.php");
?>
<form action="" method="POST">
<select name="opstine" class="form-control" id="select_id" onchange="getNaselja(this.value)">
<option>..Izaberite Opstinu..</option>
<?php foreach($opstineArr as $key => $opstina): ?>
<option value="<?php echo $opstina['OpstinaID']; ?>" <?php if(isset($opstine) && $opstine==$opstina['OpstinaID']) echo "selected"; ?> ><?php echo $opstina['NazivOpstine']; ?></option>
<?php endforeach; ?>
</select>
<?php if(isset($error["opstine"])) echo $error["opstine"]; ?>
<p>
<select name='naselja' id='naseljeLista' class='form-control' style='margin-top:10px;'>
</select>
<span><?php if(isset($error["naselja"])) echo $error["naselja"]; ?></span>
</p><br>
<input type="text" name="ime" value="<?php if(isset($ime)) echo $ime; ?>" class="form-control col-md-7 col-xs-12"><?php if(isset($error["ime"])) echo $error["ime"]; ?><br><br>
<input type="submit" name="addNesto" class="btn btn-sm btn-success">
</form>
<?php include("includes/footer.php"); ?>
getNaselja.php
global $conn;
include("includes/conn.php");
if(!empty($_POST["opstina_id"])){
$opstinaID = $_POST["opstina_id"];
$sql1 = "SELECT * FROM naselje WHERE OpstinaID=".$opstinaID;
$result1 = $conn->query($sql1);
if($result1->num_rows > 0){
$naseljaArr = array();
while ($one = $result1->fetch_assoc()) {
$naseljaArr[] = $one;
}
}
echo "<option value=''>---Izaberite naselje---</option>";
foreach ($naseljaArr as $key => $value) {
if(isset($_POST["naselja"]) && $value["NaseljeID"]==$_POST["naselja"]){
echo "<option value='".$value['NaseljeID']."' selected='selected' style='display:block;'>".$value['NazivNaselja']."</option>";
}else{
echo "<option value='".$value['NaseljeID']."'>".$value['NazivNaselja']."</option>";
}
}
}
footer.php
<script>
function getNaselja(val){
$.ajax({
type: 'POST',
url: 'getNaselja.php',
data: 'opstina_id='+val,
success: function(data){
$('#naseljeLista').html(data);
console.log(data);
}
});
}
</script>
example of form after submit on index.php
When I choose from first select my data on the console looks like:
<option value=''>---Izaberite naselje---</option>
<option value='4610'>Beška</option>
<option value='4611'>Inđija</option>
<option value='4612'>Jarkovci</option>
<option value='4613'>Krčedin</option>
<option value='4614'>Ljukovo</option>
<option value='4615'>Maradik</option>
<option value='4616'>Novi Karlovci</option>
<option value='4617'>Novi Slankamen</option>
<option value='4618'>Slankamenački Vinogradi</option>
<option value='4619'>Stari Slankamen</option>
<option value='4620'>Čortanovci</option>