How do I format the string to POST data through XMLHttpRequest in Laravel?

I’m trying to send my data through XMLHttpRequest but don’t know how to format the string with all the data

My JS Code:

function savePhotos() {
    var csrf = document.querySelector('meta[name="_token"]').content;
    var xhr = new XMLHttpRequest();
    xhr.open("POST", saveRoute, true);
    xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8");
    xhr.setRequestHeader("X-CSRF-TOKEN", csrf); 
    xhr.send("name='test'"); //What do I put here
}

My Controller create function:

 public function create(Request $request)
 {
     $data = $request->all();
     $model = Photo::create([
            'categoryId' => $data['categoryId'],
            'collectionId' => $data['collectionId'],
            'categoryId' => $data['categoryId'],
            'name' => $data['name'],
            'views' => $data['views'],
            'likes' => $data['likes'],
            'dateUploaded' => $data['dateUploaded'],
            'altText' => $data['altText'],
            'url' => $data['url'],
            'private' => $data['private'],
         ]);
       return redirect()->route("photoIndex");
    }