client id

item.rb

class Item < ActiveRecord::Base
end

items.js.coffee

$(document).on 'submit', '#new_item', (e) ->
  e.preventDefault()
  
  $.ajax
    type: 'POST'
    url: '/items'
    dataType: 'json'
    data: $(this).serialize()
    beforeSend: (xhr) =>
      xhr.cid = Date.now()
      $(this).after "<article id='#{xhr.cid}'> #{item_name.value} </article>"
      @reset()
    success: (item, status, xhr) ->
      $("##{xhr.cid}").replaceWith "<article id='#{item.id}'> #{item.name} </article>"

items_controller.rb

class ItemsController < ApplicationController
  respond_to :json
  
  def create
    @item = Item.create(item_params)
    respond_with @item
  end
  
private

  def item_params
    params.require(:item).permit(:name)
  end
end