Tutorial

Create a reactive Twitter clone in pure Ruby

In this step-by-step guide, I will show you how to create a Twitter clone in pure Ruby with Matestack, following the great screencasts from Chris McCord Phoenix LiveView Twitter Clone and Nate Hopkins Stimulus Reflex Twitter Clone. We will use the Gem matestack-ui-core, which enables us to implement our UI in some Ruby classes rather than writing ERB, HAML or Slim views. Furthermore we don't need to touch JavaScript in order to create reactive UI features, such as updating the DOM without a full browser page reload or syncing multiple web clients through Action Cable!

I've added a small demo showing you what you will be creating in this tutorial:

This guide utilizes the full power of Matestack and uses matestack-ui-core as a complete substitute for Rails views. If you only want to create UI components in pure Ruby on existing Rails views, please check out this guide

The code for this twitter clone tutorial is available in this repository.

Setup

rails new twitter_clone --webpacker
cd twitter_clone
bundle add matestack-ui-core
yarn add matestack-ui-core
rails g scaffold Post body:text likes_count:integer username:string

Model & Database

db/migrate/12345_create_posts.rb

class CreatePosts < ActiveRecord::Migration[6.0]
  def change
    create_table :posts do |t|
      t.text :body
      t.integer :likes_count, default: 0 # add default
      t.string :username

      t.timestamps
    end
  end
end
rails db:migrate

app/models/post.rb

class Post < ApplicationRecord

  default_scope { order(created_at: :desc) }

  validates :body, presence: true, allow_blank: false
  validates :username, presence: true

end

Import Matestack's JavaScript

Previously, in version 1.5, Vue and Vuex were imported automatically. Now this must be done manually which is the webpacker way. You can import it in app/javascript/packs/application.js or in another pack if you need.

app/javascript/packs/application.js

// This file is automatically compiled by Webpack, along with any other files
// present in this directory. You're encouraged to place your actual application logic in
// a relevant structure within app/javascript and only use these pack files to reference
// that code so it'll be compiled.

require("@rails/ujs").start()
// require("turbolinks").start() //remove
require("@rails/activestorage").start()
require("channels")

import Vue from 'vue/dist/vue.esm'
import Vuex from 'vuex'

import MatestackUiCore from 'matestack-ui-core'

let matestackUiApp = undefined

document.addEventListener('DOMContentLoaded', () => {
  matestackUiApp = new Vue({
    el: "#matestack-ui",
    store: MatestackUiCore.store
  })
})

Application Layout and Views

On app/views/layouts/application.html.erb do:

app/views/layouts/application.html.erb

<!DOCTYPE html>
<html>
  <head>
    <title>TwitterClone</title>
    <meta name="viewport" content="width=device-width,initial-scale=1,shrink-to-fit=no">
    <%= csrf_meta_tags %>
    <%= csp_meta_tag %>

    <meta charset="utf-8">

    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">

    <%= stylesheet_link_tag 'application', media: 'all' %>
    <%= javascript_pack_tag 'application' %>
  </head>

  <body>
    <div id="matestack-ui">
      <%= yield %>
    </div>
  </body>
</html>

Controller

app/controllers/application_controller.rb

class ApplicationController < ActionController::Base

  include Matestack::Ui::Core::Helper

end

app/controllers/posts_controller.rb

class PostsController < ApplicationController

  # GET /posts
  # GET /posts.json
  def index
    @posts = Post.all
  end

  # POST /posts
  # POST /posts.json
  def create
    @post = Post.new(post_params)

    respond_to do |format|
      if @post.save
        format.html { redirect_to @post, notice: 'Post was successfully created.' }
        format.json { render :show, status: :created, location: @post }
      else
        format.html { render :new }
        format.json { render json: @post.errors, status: :unprocessable_entity }
      end
    end
  end

  private

  # Only allow a list of trusted parameters through.
  def post_params
    params.require(:post).permit(:username, :body)
  end

end

Matestack App and Pages

mkdir -p app/matestack/twitter_clone
touch app/matestack/twitter_clone/app.rb
mkdir -p app/matestack/twitter_clone/pages/posts
touch app/matestack/twitter_clone/pages/posts/index.rb

app/matestack/twitter_clone/app.rb

class TwitterClone::App < Matestack::Ui::App

  def response
    div class: "container" do
      heading size: 1, text: "Twitter Clone", class: "mb-5"
      yield if block_given?
    end
  end

end

app/matestack/twitter_clone/pages/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  def prepare
    @posts = Post.all
  end

  def response
    @posts.each do |post|
      div class: "mb-3 p-3 rounded shadow-sm" do
        heading size: 5 do
          plain post.username
          small text: post.created_at.strftime("%d.%m.%Y %H:%M")
        end
        paragraph text: post.body
      end
    end
  end

end

Add Matestack to the Controller

app/controllers/posts_controller.rb

class PostsController < ApplicationController

  matestack_app TwitterClone::App # add this

  # GET /posts
  # GET /posts.json
  def index
    # @posts = Post.all
    render TwitterClone::Pages::Posts::Index # add this
  end

  # ...
end

Test the current state

rails s

You should see the heading "Twitte Clone" and that's it. We don't have any posts in our database, so we need a form to create one!

Add a Reactive Form

app/matestack/twitter_clone/pages/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  def prepare
    @posts = Post.all
  end

  def response
    post_form_partial
    post_list_partial
  end

  private

  def post_form_partial
    div class: "mb-3 p-3 rounded shadow-sm" do
      heading size: 4, text: "New Post", class: "mb-3"
      matestack_form form_config_helper do
        div class: "mb-3" do
          form_input key: :username, type: :text, placeholder: "Username", class: "form-control"
        end
        div class: "mb-3" do
          form_textarea key: :body, placeholder: "What's up?", class: "form-control"
        end
        div class: "mb-3" do
          button 'submit', type: :submit, class: "btn btn-primary", text: "Post!"
        end
      end
    end
  end

  def form_config_helper
    {
      for: Post.new, path: posts_path, method: :post,
      # optional: in order to map Bootstrap's CSS classes, you can adjust the form error rendering like so:
      errors: {wrapper: {tag: :div, class: 'invalid-feedback'}, input: {class: 'is-invalid'}}
    }
  end

  def post_list_partial
    @posts.each do |post|
      div class: "mb-3 p-3 rounded shadow-sm" do
        heading size: 5 do
          plain post.username
          small text: post.created_at.strftime("%d.%m.%Y %H:%M")
        end
        paragraph text: post.body
      end
    end
  end

end

app/controllers/posts_controller.rb

class PostsController < ApplicationController

  # ...

  # POST /posts
  # POST /posts.json
  def create
    @post = Post.new(post_params)

    # respond_to do |format|
    #   if @post.save
    #     format.html { redirect_to @post, notice: 'Post was successfully created.' }
    #     format.json { render :show, status: :created, location: @post }
    #   else
    #     format.html { render :new }
    #     format.json { render json: @post.errors, status: :unprocessable_entity }
    #   end
    # end

    if @post.save
      render json: {
        message: 'Post was successfully created.'
      }, status: :created
    else
      render json: {
        errors: @post.errors,
        message: 'Post could not be created.'
      }, status: :unprocessable_entity
    end
  end

  # ...

end

Test the current state

You should see a basic index page with a form at the top. When submitting the form without any values, ActiveRecord errors should appear below the input fields without a browser page reload. When submitting valid data, the form should reset automatically without a browser page reload, but you will still have to reload the browser in order to see the new post!

To get that reactivity to work, we need make use of the async component.

Add Matestack's Async Component

app/matestack/twitter_clone/pages/posts/index.rb

# ...

def form_config_helper
  {
    for: Post.new, path: posts_path, method: :post,
    errors: {
      wrapper: {tag: :div, class: 'invalid-feedback'},
      input: {class: 'is-invalid'}
    },
    success: {emit: "submitted"}
  }
end

def post_list_partial
  async rerender_on: "submitted", id: "post-list" do
    @posts.each do |post|
      div class: "mb-3 p-3 rounded shadow-sm" do
        heading size: 5 do
          plain post.username
          small text: post.created_at.strftime("%d.%m.%Y %H:%M")
        end
        paragraph text: post.body
      end
    end
  end
end

# ...

Test the current state

Cool! Now you should see the list automatically updating itself after form submission without a browser page reload! And we didn't have to write any JavaScript. Just two lines of simple Ruby code! How cool is that?

Now we need to add some action components in order to "like" the posts.

Enable "likes"

config/routes.rb

Rails.application.routes.draw do
  resources :posts do
    member do
      put 'like', to: 'posts#like'
    end
  end
end

app/controllers/posts_controller.rb

# ...

# PUT /posts/1/like
def like
  @post = Post.find params[:id]
  @post.increment(:likes_count)

  if @post.save
    render json: {
      message: 'Post was successfully liked.'
    }, status: :created
  else
    render json: {
      errors: @post.errors,
      message: 'Post could not be liked.'
    }, status: :unprocessable_entity
  end
end

# ...

app/matestack/twitter_clone/pages/index.rb

# ...

def post_list_partial
  async rerender_on: "submitted", id: "post-list" do
    @posts.each do |post|
      post_partial(post)
    end
  end
end

def post_partial(post)
  async rerender_on: "liked_post_#{post.id}", id: "post-#{post.id}" do
    div class: "mb-3 p-3 rounded shadow-sm" do
      heading size: 5 do
        plain post.username
        small text: post.created_at.strftime("%d.%m.%Y %H:%M")
      end
      paragraph text: post.body, class: "mb-5"
      action path: like_post_path(post), method: :put, success: {emit: "liked_post_#{post.id}"} do
        button class: "btn btn-light" do
          plain "Like (#{post.likes_count})"
        end
      end
    end
  end
end

# ...

Test the current state

When you click the "Like" button on a post, you will see the counter increasing without a full page reload! Again: Reactivity without any JavaScript!

Great! We added a reactive form and reactive actions. We can now add some reactive feedback on top using the toggle component!

Add Reactive Feedback Using the toggle Component

app/matestack/twitter_clone/pages/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  def prepare
    @posts = Post.all
  end

  def response
    post_form_partial
    post_list_partial
  end

  private

  def post_form_partial
    div class: "mb-3 p-3 rounded shadow-sm" do
      heading size: 4, text: "New Post", class: "mb-3"
      matestack_form form_config_helper do
        # ...
      end
    end
    toggle show_on: "submitted", hide_after: 5000 do
      div class: "container fixed-bottom w-100 bg-success text-white p-3 rounded-top" do
        heading size: 4, text: "Success: {{ event.data.message }}"
      end
    end
    toggle show_on: "form_failed", hide_after: 5000 do
      div class: "container fixed-bottom w-100 bg-danger text-white p-3 rounded-top" do
        heading size: 4, text: "Error: {{ event.data.message }}"
      end
    end
  end

  def form_config_helper
    {
      for: Post.new, path: posts_path, method: :post,
      success: {emit: "submitted"},
      failure: {emit: "form_failed"},
      errors: {wrapper: {tag: :div, class: 'invalid-feedback'}, input: {class: 'is-invalid'}}
    }
  end

  # ...

end

Test the current state

Great! Now we get instant feedback after performing successful or unsuccessful form submissions! And still no line of JavaScript involved! The same approach would work for our actions, but we do not want to have that feedback after performing the actions in this example!

All of the above described reactivity only applies for one client. A second user wouldn't see the new post, unless he reloads his browser page. But of course, we want to sync all connected clients! It's time to integrate ActionCable!

Integrate Action Cable

rails generate channel MatestackUiCoreChannel

app/javascript/channels/matestack_ui_core_channel.js

import consumer from "./consumer"
import MatestackUiCore from 'matestack-ui-core'

consumer.subscriptions.create("MatestackUiCoreChannel", {
  connected() {
    // Called when the subscription is ready for use on the server
  },

  disconnected() {
    // Called when the subscription has been terminated by the server
  },

  received(data) {
    // Called when there's incoming data on the websocket for this channel
    MatestackUiCore.eventHub.$emit(data.event, data)
  }
});

app/channels/matestack_ui_core_channel.rb

class MatestackUiCoreChannel < ApplicationCable::Channel
  def subscribed
    stream_from "matestack_ui_core"
  end

  def unsubscribed
    # Any cleanup needed when channel is unsubscribed
  end
end

app/controllers/posts_controller.rb

# ...

# PUT /posts/1/like
def like
  @post = Post.find params[:id]
  @post.increment(:likes_count)

  if @post.save
    ActionCable.server.broadcast('matestack_ui_core', {
      event: "cable__liked_post_#{@post.id}"
    })
    render json: {
      message: 'Post was successfully liked.'
    }, status: :created
  else
    render json: {
      errors: @post.errors,
      message: 'Post could not be liked.'
    }, status: :unprocessable_entity
  end
end

# POST /posts
def create
  @post = Post.new(post_params)

  if @post.save
    ActionCable.server.broadcast('matestack_ui_core', {
      event: 'cable__created_post'
    })
    render json: {
      message: 'Post was successfully created.'
    }, status: :created
  else
    render json: {
      errors: @post.errors,
      message: 'Post could not be created.'
    }, status: :unprocessable_entity
  end
end

# ...

app/matestack/twitter_clone/pages/posts/index.rb

# ...

def form_config_helper
  {
    for: Post.new, path: posts_path, method: :post,
    success: {emit: "submitted"},
    failure: {emit: "form_failed"},
    errors: {wrapper: {tag: :div, class: 'invalid-feedback'}, input: {class: 'is-invalid'}}
  }
end

def post_list_partial
  async rerender_on: "cable__created_post", id: "post-list" do
    @posts.each do |post|
      post_partial(post)
    end
  end
end

# ...

app/matestack/twitter_clone/pages/index.rb

# ...

def post_list_partial
  @posts.each do |post|
    post_partial(post)
  end
end

def post_partial post
  # async rerender_on: "liked_post_#{post.id}", id: "post-#{post.id}" do
  async rerender_on: "cable__liked_post_#{post.id}", id: "post-#{post.id}" do
    div class: "mb-3 p-3 rounded shadow-sm" do
      heading size: 5 do
        plain post.username
        small text: post.created_at.strftime("%d.%m.%Y %H:%M")
      end
      paragraph text: post.body, class: "mb-5"
      # action path: like_post_path(post), method: :put, success: {emit: "liked_post_#{post.id}"} do
      action path: like_post_path(post), method: :put do
        button class: "btn btn-light" do
          plain "Like (#{post.likes_count})"
        end
      end
    end
  end
end

# ...

Test the current state

Wow! We just had to copy and paste a JavaScript snippet once in order to integrate ActionCable, broadcast an event from the controller action and without any more added complexity, we get synced clients, implemented in pure Ruby! Fantastic!

We will take a short break before adding the next cool reactivity feature and refactor a little bit! Matestack encourages you to create a readable and maintainable UI implemetation. Therefore we will move some complexity from the current index page to a self contained Matestack component!

Create a Matestack Component

mkdir -p app/matestack/components
touch app/matestack/components/post.rb

app/matestack/components/post.rb

class Components::Post < Matestack::Ui::Component

  requires :post

  def response
    # copied from the index page
    async rerender_on: "cable__liked_post_#{context.post.id}", id: "post-#{context.post.id}" do
      div class: "mb-3 p-3 rounded shadow-sm" do
        heading size: 5 do
          plain context.post.username
          small text: context.post.created_at.strftime("%d.%m.%Y %H:%M")
        end
        paragraph text: context.post.body, class: "mb-5"
        action path: like_post_path(context.post), method: :put do
          button class: "btn btn-light" do
            plain "Like (#{context.post.likes_count})"
          end
        end
      end
    end
  end

end

app/matestack/twitter_clone/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  def prepare
    @posts = Post.all
  end

  def response
    post_form_partial
    post_list_partial
  end

  private

  # ...

  def post_list_partial
    async rerender_on: "submitted", id: "post-list" do
      @posts.each do |post|
        # post_partial(post)
        Components::Post.(post: post)
      end
    end
  end

  # def post_partial post
  #   async rerender_on: "cable__liked_post_#{post.id}", id: "post-#{post.id}" do
  #     div class: "mb-3 p-3 rounded shadow-sm" do
  #       heading size: 5 do
  #         plain post.username
  #         small text: post.created_at.strftime("%d.%m.%Y %H:%M")
  #       end
  #       paragraph text: post.body, class: "mb-5"
  #       action path: like_post_path(post), method: :put do
  #         button class: "btn btn-light" do
  #           plain "Like (#{post.likes_count})"
  #         end
  #       end
  #     end
  #   end
  # end

end

Test the current state

Everything should be the same! We just refactored some code in order to better manage complexity.

Component Registry

Components can be invoked as we have done above (Components::Post.(post: post)). But sometimes the namespace can get a little long and in the interest of keeping our code beautiful, we can register our components so we can call them like:

  # ...

  def post_list_partial
    async rerender_on: "submitted", id: "post-list" do
      @posts.each do |post|
        # post_partial(post)
        post_component post: post
      end
    end
  end

  # ...

Let's refactor and set up a component registry and register our component.

touch app/matestack/components/registry.rb

app/matestack/components/registry.rb

module Components::Registry

  def post_component(post:)
    Components::Post.(post: post)
  end

end

app/matestack/twitter_clone/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  include Components::Registry

  def prepare
    @posts = Post.all
  end

  def response
    post_form_partial
    post_list_partial
  end

  private

  # ...

  def post_list_partial
    async rerender_on: "submitted", id: "post-list" do
      @posts.each do |post|
        # post_partial(post)
        post_component post: post
      end
    end
  end

  # ...

end

Test the current state again

Everything should be the same after this small refactoring.

The Cable Component

Now we will cover the last topic of this guide:

As described before, the async rerenders it's whole body. The async wrapping the whole post list therefore rerenders ALL posts. If our list of posts grows, the performance of the rerendering will decrease. In a lot of usecases, this will not be an issue since the UI is not too big/too complex. So go ahead and use async everywhere you're not rerendering big or complex UIs and enjoy the simplicity of that rerendering approach!

But now imagine, your post list will be too big at some point. We should switch the reactivity approach to a more granular one. Let's use the cable component alongside our already added ActionCable introduction and reuse pretty much all written code!

Use the cable Component For List Rerendering

app/matestack/twitter_clone/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  def prepare
    @posts = Post.all
  end

  def response
    post_form_partial
    post_list_partial
  end

  private

  # ...

  def post_list_partial
    # async rerender_on: "submitted", id: "post-list" do
    cable prepend_on: "cable__created_post", id: "post-list" do
      @posts.each do |post|
        post_component post: post
      end
    end
  end

end

app/controllers/posts_controller.rb

# ...

# POST /posts
def create
  @post = Post.new(post_params)

  if @post.save
    ActionCable.server.broadcast('matestack_ui_core', {
      event: 'cable__created_post',
      data: post_component(post: @post) # add this line
    })
    render json: {
      message: 'Post was successfully created.'
    }, status: :created
  else
    render json: {
      errors: @post.errors,
      message: 'Post could not be created.'
    }, status: :unprocessable_entity
  end
end

# ...

Test the current state

You probably don't realize any difference on the UI, but now ONLY the fresh post will be rendered on the server and pushed to the cable component mounted in the browser. The cable component is configured to prepend (put on top) everything pushed from the server on the cable__created_post event. This reactivity approach is now already much more scalable in a context of big/complex UI rerendering.

The cable component can prepend, append, update and delete elements within its body or replace its whole body with something pushed from the server. We want to use the update feature in order to rerender a specific post when liked:

Adjust the cable Component for Post Rerendering

app/matestack/twitter_clone/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  def prepare
    @posts = Post.all
  end

  def response
    post_form_partial
    post_list_partial
  end

  private

  # ...

  def post_list_partial
    # cable prepend_on: "cable__created_post", id: "post-list" do
    cable prepend_on: "cable__created_post", update_on: "cable__liked_post", id: "post-list" do
      @posts.each do |post|
        post_component post: post
      end
    end
  end

end

app/matestack/components/post.rb

class Components::Post < Matestack::Ui::Component

  requires :post

  def response
    # async rerender_on: "cable__liked_post_#{post.id}", id: "post-#{context.post.id}" do
      div class: "mb-3 p-3 rounded shadow-sm", id: "post-#{context.post.id}" do
        heading size: 5 do
          plain context.post.username
          small text: context.post.created_at.strftime("%d.%m.%Y %H:%M")
        end
        paragraph text: context.post.body, class: "mb-5"
        action path: like_post_path(context.post), method: :put do
          button class: "btn btn-light" do
            plain "Like (#{context.post.likes_count})"
          end
        end
      end
    # end
  end

end

app/controllers/posts_controller.rb

# ...

# PUT /posts/1/like
def like
  @post = Post.find params[:id]
  @post.increment(:likes_count)

  if @post.save
    ActionCable.server.broadcast('matestack_ui_core', {
      # event: "cable__liked_post_#{@post.id}"
      # no id required in the event name, the cable component will figure out which post
      # should be updated using the root element ID of the pushed component
      event: "cable__liked_post", # change the event name
      data: post_component(post: @post) # add this line
    })
    render json: {
      message: 'Post was successfully liked.'
    }, status: :created
  else
    render json: {
      errors: @post.errors,
      message: 'Post could not be liked.'
    }, status: :unprocessable_entity
  end
end

# POST /posts
def create
  @post = Post.new(post_params)

  if @post.save
    ActionCable.server.broadcast('matestack_ui_core', {
      event: 'cable__created_post',
      data: post_component(post: @post)
    })
    render json: {
      message: 'Post was successfully created.'
    }, status: :created
  else
    render json: {
      errors: @post.errors,
      message: 'Post could not be created.'
    }, status: :unprocessable_entity
  end
end

# ...

Test the current state

Again: you probably don't realize any difference on the UI, but now ONLY the updated post will be rendered on the server and pushed to the cable component mounted in the browser.

The cable component is configured to update the component pushed from the server on the cable__liked_post event. The cable component then reads the ID of the root element of the pushed component, looks for that ID within it's body and updates this element with the pushed component.

Now, we're rerendering the list and its elements completely with the cable component. As described, this is an ALTERNATIVE approach to the introduced async component approach. The cable component requires a bit more implementation and brain power but makes our reactivity more scalable. Use the cable component wherever you think async would be too slow at some point!

Ok, let's lazy load the list of posts in order to speed up initial page load when reading the posts from the database and rendering them gets "too slow" at some point. Take a deep breath: We will use async and cable together now!

Relax, it's super simple:

Lazy Load the Post List With Async's defer Feature

app/matestack/twitter_clone/posts/index.rb

class TwitterClone::Pages::Posts::Index < Matestack::Ui::Page

  # def prepare
  #   @posts = Post.all
  # end

  def response
    post_form_partial
    post_list_partial
  end

  private

  # ...

  def posts
    Post.all
  end

  def post_list_partial
    async defer: true, id: "deferred-post-list" do
      cable prepend_on: "cable__created_post", update_on: "cable__liked_post", id: "post-list" do
        # @posts.each do |post|
        posts.each do |post|
          post_component post: post
        end
      end
    end
  end

end

Test the current state

That was easy, right? The async requested its content right after the page was loaded. We moved the ActiveRecord query out of the prepare method out of following reason: When rendering a Matestack page/component, the prepare method is always called. This means, the ActiveRecord query is performed on the initial page load although we don't need the data yet. Matestacks rendering mechanism stops rendering components which are wrapped in an async defer component on initial page load and only renders them, when they are explicitly requested in a subsequent HTTP call. Therefore we should take care of calling the ActiveRecord query only from within the deferred block. In our example we accomplish this by calling the helper method posts instead of using the instance variable @posts, formerly resolved in the prepare method.

Using this approach, it is super simple to speed up initial page loads without adding complexity or JavaScript to your code! Awesome!

Want some sugar? How about adding a CSS animation while lazy loading the post list?

mkdir -p app/javascript/packs/stylesheets
touch app/javascript/packs/stylesheets/application.scss

app/javascript/packs/stylesheets/application.scss

// Async loading state
.matestack-async-component-container{

  opacity: 1;
  transition: opacity 0.2s ease-in-out;

  &.loading {
    opacity