issue in special character converting in jquery - php

Question

I have use ajax to get a code from the database.
In my database shows my answer Nmap –T4 –F 10.15.0.0/24
and when ajax get that it shows Nmap �T4 �F 10.15.0.0/24 in my console.
I have use decodeEntities() for that but it is not working. I have put my coe below.
$.post('functions.php', {answer: answer, ID: ID, action: action, email: email, TestName:TestName}, function(response)
{
var data = decodeEntities(response);
console.log(data);
});
function decodeEntities(encodedString) {
var textArea = document.createElement('textarea');
textArea.innerHTML = encodedString;
return textArea.value;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>
function category_array($con,$quiz_category){
$final_array = array();
foreach ($quiz_category as $row) {
$category = find_categoryname($row);
//print_r($category); die();
$query ="SELECT * FROM `$row` WHERE `ID` IN(18,205,166)";
$query_result = mysqli_query($con,$query);
if(mysqli_num_rows($query_result)) {
while($row = mysqli_fetch_assoc($query_result)){
$row["question_category"] = $category;
$final_array[] = utf8_converter($row);
//print_r($row); die();
}
}
//$final_array[] = $result_array;
}
return $final_array;
}
function utf8_converter($array){
array_walk_recursive($array, function(&$item, $key){
if(!mb_detect_encoding($item, 'utf-8', true)){
$item = utf8_encode($item);
}
});
return $array;
}