Parse php array('s) to json isn't work - php

Question

I've created a function in CakePHP 3 to get a list of content and a list of labels for a dynamic filled html table. But after I parsed the php array's to json the labels array isn't parsed. This will give me the "Cannot use 'in' operator...." error from the DataTables library.
When I log the parsed array you can see below that 'labels' is a normal array and content is a json array. I need two json array's.
{labels: Array(6), content: {…}}
Parse php array to json inside my controller:
public function ajaxGetContentList() {
$allContent = this.getAllData();
$contentArray = array();
$labelArray = array();
foreach ($allContent as $content) {
if (isset($content->element->display)) {
$contentArray[$content->form_id][$content->element->name] = $content->content;
if(!in_array( $content->element->name, $labelArray)){
$labelArray[] = $content->element->name;
}
}
}
$data = [
'labels' => $labelArray,
'content' => $contentArray
];
$content = json_encode($data);
$this->response->getBody()->write($content);
$this->response = $this->response->withType('json');
return $this->response;
}
}
Ajax call inside my view:
function setContentListToTable() {
$.ajax({
url: websiteUrl + 'storages/list/' + '<?= $slug; ?>' + '/ajaxGetContentList',
type: 'post',
dataType: 'html',
data: {slug: '<?= $slug; ?>'},
success: function (data) {
var jsonArray = jQuery.parseJSON(data)
$('table').DataTable({ "columns": jsonArray.labels,"data": jsonArray.content});
}
});
}