combobox ajax (PHP)

<div class="form-group">
        <label class="control-label col-xs-3">Layanan</label>
        <div class="col-xs-2">
            <?php
            $query = "SELECT * FROM kategori ORDER BY id_kategori ASC";
            $result = mysqli_query($connect,$query);
            ?>
            <select name=kategori id="id_kategori" onchange="kategori(id_kategori.value)">
                <option>-- Pilih Kategori --</option>
                <?php
                while($r = mysqli_fetch_assoc($connect,$result)){
                ?>
                <option value="<?php echo $r['id_kategori'] ?>"><?php echo $data['kategori'] ?></option>
                <?php } ?>
            </select>
            <div id="kategori-view"></div>
        </div>
        <div class="col-xs-2">
            <?php
                $kode = $_GET['id_kategori'];
                $query = "SELECT * FROM layanan WHERE id_layanan = '".$id_layanan."' ORDER BY id_layanan ASC";
                $result = mysqli_query($connect, $query);
            ?>
            <select name="layanan" id="id_layanan" onChange="layanan(id_layanan.value)">
            <option value="">-- Pilih Layanan --</option>
            <?php
                while($r = mysqli_fetch_array($connect,$result)){
            ?>
                <option value="<?php echo $r['id_layanan'] ?>"><?php echo $data['nama_layanan'] ?></option>
            <?php } ?>
            </select>
            <div id="layanan-view"></div>
        </div>
    </div>