How to send an array from client side javascript to node js

Question

I have a post tags functionality for my website: Tag functionallity. have a look at this code, I grab that tags with javascript and save them into tags array:

var formNewPost = $("#formNewPost");
formNewPost.on("submit", function (event) {
  var tagElements = $("span.tag span");
  var tags = [];
  for (var i = 0; i < tagElements.length; i++) {
    var text = document.querySelectorAll("span.tag span")[i].innerText;
    text = text.trim();
    tags.push(text);
  }
});

now I have my suitable array, now I wanna save that into my mongoDB database. my node js code:

  var title = req.body.title;
  var tags =  // I want that array from client side to be here
  var type = req.body.type;
  var body = req.body.body;
  var author = req.body.author;

  var newPost = {title, author, tags, type, body, author};

  Post.create(newPost, function (err, newPost) {
    if (err) {
      req.flash('error', 'An error occurred, please try again.');
      res.redirect('/posts/new');
    } else {
      req.flash('success', 'Post created successfully.');
      res.redirect('/posts');
    }
  });

But how can I do that? I tried this code but it is not working at all:

tags.push(text);
    $.ajax({
        type: "POST",
        url: '/posts',
        data: { tags : tags },
        success: function(data)
        {
            alert("success!");
        }
    });

then grab that data with express:

  var tags = req.body.tags; // AN ARRAY FROM JAVASCRIPT

But it is not working at all, what is the problem?