============================================= includes/incl.page.php =================================================
<?php

/* Answer to: "php error reporting" */

ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

$response = array(
	'status' => 0,
	'message' => 'Form submission falied, please try again'
);

if (isset($_POST["img_page"]) || isset($_POST["page_title"]) || isset($_POST["page_descr"]) || isset($_POST["videoId"])) {

	$newFileName = basename($_FILES["page_img"]["name"]);

	if (empty($newFileName)) {
		$newFileName = "pageImg";
	} else {
		//create lowercase of filename and replace empty space with -
		$newFileName = strtolower(str_replace(" ", "-", $newFileName));
	}
	$imgTitle = isset($_POST["page_title"]);
	$imgDescr = isset($_POST["page_descr"]);

	$pageImg = isset($_POST["page_img"]);

	$fileName = $_FILES["page_img"]["name"];
	$fileType = $_FILES["page_img"]['type'];
	$fileTempName = $_FILES["page_img"]['tmp_name'];
	$fileError = $_FILES["page_img"]['error'];
	$fileSize = $_FILES["page_img"]['size'];

	echo $fileName;

	$youtubeVideoId = isset($_POST["videoId"]);

	$fileExtension = explode(".", $fileName);
	$fileActualExt = strtolower(end($fileExtension));

	$allowed = array("jpg", "jpeg", "png");

	if (in_array($fileActualExt, $allowed)) {
		if ($fileError === 0) {
			if ( $fileSize < 2000000 ){
				$imageFullName = $newFileName . "." . uniqid("", true) . "." . $fileActualExt;
				$fileDestination = "../img/page/" . $imageFullName;

				include_once "dbh.incl.php";

				if (empty($imgTitle) || empty($imgDescr) || empty($youtubeVideoId)) {
					header("Location: ../page-post.php?upload=emptyinput" . $youtubeVideoId . "");
					exit();
				} else {
					$sql = "SELECT * FROM pages";
					$stmt = mysqli_stmt_init($conn);
					if (!mysqli_stmt_prepare($stmt, $sql)) {
						echo"SQL statement gefaald 1!";
					} else {
						mysqli_stmt_execute($stmt);
						$result = mysqli_stmt_get_result($stmt);
//						$rowCount = mysqli_num_rows($result);
//						$setImageOrder = $rowCount + 1;

						$sql = "INSERT INTO pages (titlePage, descPage, imgPage, youtubeVideoId) VALUES (?, ?, ?, ?)";
						if (!mysqli_stmt_prepare($stmt, $sql)) {
						echo "SQL statement gefaald 2!";
						}
						else {
							// bind 3 strings to statement
							mysqli_stmt_bind_param($stmt, "ssss", $imgTitle, $imgDescr, $imageFullName, $youtubeVideoId);
							mysqli_stmt_execute($stmt);

							move_uploaded_file($fileTempName, $fileDestination);

							header("Location: ../page-manage.php?upload=succes");
							exit();
						}
					}
				}


			} else {
				$response['message'] = 'bestand is te groot!';
			}

		} else {
			$response['message'] = 'U heeft een error bij het uploaden van uw bestand!';
		}
	} else {
		$response['message'] = 'Om een bestand te uploaden moet het een PNG/JPEG/JPG bestand zijn!';
	}

	echo json_decode($response);
} else {
	$response['message'] = 'Form input not valid';
}

echo json_encode($response);



======================================== ajax.js =====================================================

 $("#myForm").on('submit', function(e){
                e.preventDefault();
                $.ajax({
                    url: '/blog-app/includes/page.incl.php',
                    type: "POST",
                    data: new FormData(this),
                    // dataType: "json",
                    cache: false,
                    processData: false,
                    contentType: false,
                    method: 'get',
                    beforesend: function() {
                        $('.submit').attr("disabled", "disabled");
                    },
                    success: function(response){
                        console.log("success", response.message);
                        alert('response', response);

                    },

                    error: function (e) {
                        alert('Something went wrong with uploading the data');
                        console.log("Unsuccessful:", e);
                    }
                });

=================================== html ========================================================

<?php
	include_once 'admin-nav.php';
	include_once 'admin-page-header.php';
	// require "includes/page.incl.php";
?>

<main class="my-5">

<div class="col-sm-10">
	<div class="container">
		<div class="align-self-center">
			<h1 class="font-weight-light text-center text-lg-left mt-4 mb-0">Upload pagina</h1>
			<br>
			<form action=" " method="post" id="myForm" enctype="multipart/form-data">

			<input type="text" name="page_title" class="page_title" placeholder="Pagina titel.." style="width:100%;"><br><br>
			<textarea name="page_descr" class="page_descr" id="" cols="30" placeholder="pagina beschrijving.." rows="10" style="width:100%;"></textarea>
			<hr>
			<input type="file" name="page_img" class="page_img">
			<label for="page_img">Kies een achtergrond</label>
			<br>
			<hr>
			<h3>Voeg een video toe</h3>
			<br>
			<input type="text" class="form-control" id="search" name="search" placeholder="type in gezochte video">
			<br>
			<div id="hide_video"><div id="name_video"></div></div>
			<br>
			<hr>
			<br>
			<h5 id="vidsAvailable">Videos beschikbaar</h5>
			<div class="row-xs-6 row-md-3">
				<div class="col">
					<div id="result"></div>
				</div>
			</div>
			<br>
			<hr>
				<section class="form-group">
					<button type="submit" name="page_upload" class="submit">Pagina Uploaden</button>
				</section>
			</form>
		</div>
	</div>
</div>
</main>

<!-- admin-page-header -->
</div>
<script scrc="js/youtube_api.js"></script>
<!-- <script src="js/preview-image.js"></script> -->
<?php
	require 'footer.php';
?>