title: Node.js read incoming data
body: <p>I started to learn node.js. But I am having a problem reading the incoming data.
  title, content, postId does not have any trouble while reading.
  But I can not read "categories[]"</p>
  
  <pre><code>// NEWPOST.JADE
    $("#editButton").click(function() {
        var formSerialize = $("form#newPost").serialize();
        $.ajax({
            type: 'PUT',
            url: 'auth/new-post',
            data: formSerialize
        }).done(function() {
            console.log("SUCCESS");
        }).fail(function() {
            console.log("FAIL");
        })
    });
  
  
  
  // POST.JS
      router.put('/', upload.single('image'), function (req, res, next) {
        console.log(req.body);
        console.log("new selected categories:  " + req.body.categories);
        const promise = Post.findByIdAndUpdate(
          req.body.postId,
          req.body,
          {
              new: true
          }
        );
        promise.then((post) =&gt; {
          res.json(post);
        }).catch((err) =&gt; {
          res.send(500);
        })
  
      });
  
  
  // RESULT CMD
      { title: 'post title',
        content: '&lt;p&gt;post content&lt;/p&gt;\r\n',
        'categories[]':
         [ '5a7310e7cfa4c52440957bde',
           '5a7310eccfa4c52440957bdf',
           '5a7310f0cfa4c52440957be0',
           '5a7310f5cfa4c52440957be1' ],
        postId: '5a7628be95d1d63668b9da31' }
      new selected categories:  undefined
      PUT /auth/new-post 200 209.076 ms - 2
  </code></pre>
  
  <p>Despite the arrival of new selected categories it seemed to undefined. how can i meet it.</p>
  
  <p>Thank you in advance.</p>