Cannot insert data from frontend Javascript to database using Mongoose

I want to accept user details in an html form and insert it into the database using mongoose model. Console logging in the userController.js shows that the record is undefined. Where might be the error?

FRONTEND.js

console.log('Frontend Reached');

$(document).ready(function() {

  var url = '/users/delete_user';
  var user_url = '/users/add_user';


  function load_users(e) {
    $.ajax({
      url: 'userview.ejs',
      dataType: 'text',
      type: 'post',
      ContentType: 'html',
      data: $('#user_form').serialize(), 
      success: function(data, textStatus, jQxhr) {
        console.log(data);
        $('#list').html(data);
        //$('#user_form').submit( load_users );
      },
      error: function(jqXhr, textStatus, errorThrown) {
        console.log(errorThrown);
      }
    });

    e.preventDefault();
  }

 //ADDING A USER

  $(document).on('click', '.btn btn-success', function(e) {
    e.preventDefault();
    var user_name = $("#nameinput").val();
    var user_age = $("#ageinput").val();
    console.log(user_name);
    console.log(user_age);

    $.ajax({
      url: 'userview.ejs',
      dataType: 'text',
      type: 'post',
      ContentType: 'html',
      data: {
        'user_name': user_name,
        'user_age': user_age
      },
      success: function(data, textStatus, jQxhr) {
        console.log(data);
        load_users();
      },
      error: function(jqXhr, textStatus, errorThrown) {
        console.log(errorThrown);
      }
    });

    e.preventDefault();


  }); //onclick


 
}); //document ready

This is userController.js

var User = require('../models/usermodel.js');
var userService = require('../services/userService');

var userController = {
  add: function(request, response) {
    var user_name = request.body.user_name;
    var user_age = request.body.user_age;
    console.log(user_name);   //SHOWS UNdEFINED
    var newUser = new User({
      name: user_name,
      age: user_age
    });
    console.log(newUser);
    //var userName = request.body.user_name;
    //var userAge = request.body.user_age;
    userService.add(newUser, function(err, added) {
      if (err != null) {
        response.send(500);
      } else {
        response.send(200);
      }
    });
  },

  delete: function(request, response) {

    var userId = request.body.user_id;
    userService.delete(userId, function(err, deleted) {
      if (err != null) {
        response.send(500);
      } else {
        response.send(200);
      }
    });
  }
};

module.exports = userController;

via Arjun Jain