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A collection of extensions and developer tools for ViewComponent



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View Component: extensions, examples and development tools

This repository contains various code snippets and examples related to the ViewComponent library. The goal of this project is to share common patterns and practices which we found useful while working on different projects (and which haven't been or couldn't be proposed to the upstream).

All extensions and patches are packed into a view_component-contrib meta-gem. So, to use them add to your Gemfile:

gem "view_component-contrib"
Sponsored by Evil Martians

Installation and generating generators

NOTE: We highly recommend to walk through this document before running the generator.

The easiest way to start using view_component-contrib extensions and patterns is to run an interactive generator (a custom Rails template).

All you need to do is to run:

rails app:template LOCATION=""

The command above:

  • Installs view_component-contrib gem.
  • Configure view_component paths.
  • Adds ApplicationViewComponent and ApplicationViewComponentPreview classes.
  • Configures testing framework (RSpec or Minitest).
  • Adds required JS/CSS configuration.
  • Adds a custom generator to create components.

The custom generator would allow you to create all the required component files in a single command:

bundle exec rails g view_component Example

# see all available options
bundle exec rails g view_component -h

Why adding a custom generator to the project instead of bundling it into the gem? The generator could only be useful if it fits your project needs. The more control you have over the generator the better. Thus, the best way is to make the generator a part of a project.

Organizing components, or sidecar pattern extended

ViewComponent provides different ways to organize your components: putting everyhing (Ruby files, templates, etc.) into app/components folder or using a sidecar directory for everything but the .rb file itself. The first approach could easily result in a directory bloat; the second is better though there is a room for improvement: we can move .rb files into sidecar folders as well. Then, we can get rid of the noisy _component suffixes. Finally, we can also put previews there (since storing them within the test folder is a little bit confusing):

components/                                 components/
  example_component/                          example/
    example_component.html                       component.html
  example_component.rb              →            component.rb
test/                                            preview.rb
  components/                                    index.css
    previews/                                    index.js

Thus, everything related to a particular component (except tests, at least for now) is located within a single folder.

The two base classes are added to follow the Rails way: ApplicationViewComponent and ApplicationViewComponentPreview.

We also put the components folder into the app/frontend folder, because app/components is too general and could be used for other types of components, not related to the view layer.

Here is an example Rails configuration:

config.autoload_paths << Rails.root.join("app", "frontend", "components")

Organizing previews

First, we need to specify the lookup path for previews in the app's configuration:

config.view_component.preview_paths << Rails.root.join("app", "frontend", "components")

By default, ViewComponent requires preview files to have _preview.rb suffix, and it's not configurable (yet). To overcome this, we have to patch the ViewComponent::Preview class:

# you can put this into an initializer
ActiveSupport.on_load(:view_component) do
  ViewComponent::Preview.extend ViewComponentContrib::Preview::Sidecarable

Reducing previews boilerplate

In most cases, previews contain only the default example and a very simple template (= render**options)). We provide a ViewComponentContrib::Preview class, which helps to reduce the boilerplate by re-using templates and providing a handful of helpers.

The default template shipped with the gem is as follows:

<div class="<%= container_class %>">
  <%- if component -%>
    <%= render component %>
  <%- else -%>
    Failed to infer a component from the preview: <%= error %>
  <%- end -%>

To define your own default template:

class ApplicationViewComponentPreview < ViewComponentContrib::Preview::Base
  # ...
  self.default_preview_template = "path/to/your/template.html.{erb,haml,slim}"
  # ...

Let's assume that you have the following ApplicationViewComponentPreview:

class ApplicationViewComponentPreview < ViewComponentContrib::Preview::Base
  # Do not show this class in the previews index
  self.abstract_class = true

It allows to render a component instances within a configurable container. The component could be either created explicitly in the preview action:

class Banner::Preview < ApplicationViewComponentPreview
  def default
    render_component "Welcome!")

Or implicitly:

class LikeButton::Preview < ApplicationViewComponentPreview
  def default
    # Nothing here; the preview class would try to build a component automatically
    # calling ``

To provide the container class, you should either specify it in the preview class itself or within a particular action by calling #render_with:

class Banner::Preview < ApplicationViewComponentPreview
  self.container_class = "absolute w-full"

  def default
    # This will use `absolute w-full` for the container class
    render_component "Welcome!")

  def mobile
      component: "Welcome!").with_variant(:mobile),
      container_class: "w-25"

If you need more control over your template, you can add a custom preview.html.* template (which will be used for all examples in this preview), or even create an example-specific previews/example.html.* (e.g. previews/mobile.html.erb).

Organizing assets (JS, CSS)

*NOTE: This section assumes the usage of Webpack, Vite or other frontend builder (e.g., not Sprockets).

We store JS and CSS files in the same sidecar folder:


The index.js is the controller's entrypoint; it imports the CSS file and may contain some JS code:

import "./index.css"

In the root of the components folder we have the index.js file, which loads all the components:

// components/index.js
const context = require.context(".", true, /index.js$/)

Using with StimulusJS

You can define Stimulus controllers right in the index.js file using the following approach:

import "./index.css"
// We reserve Controller for the export name
import { Controller as BaseController } from "stimulus";

export class Controller extends BaseController {
  connect() {
    // ...

Then, we need to update the components/index.js to automatically register controllers:

// We recommend putting Stimulus application instance into its own
// module, so you can use it for non-component controllers

// init/stimulus.js
import { Application } from "stimulus";
export const application = Application.start();

// components/index.js
import { application } from "../init/stimulus";

const context = require.context(".", true, /index.js$/)
context.keys().forEach((path) => {
  const mod = context(path);

  // Check whether a module has the Controller export defined
  if (!mod.Controller) return;

  // Convert path into a controller identifier:
  //   example/index.js -> example
  //   nav/user_info/index.js -> nav--user-info
  const identifier = path.replace(/^\.\//, '')
    .replace(/\/index\.js$/, '')
    .replace(/\//g, '--');

  application.register(identifier, mod.Controller);

We also can add a helper to our base ViewComponent class to generate the controller identifier following the convention above:

class ApplicationViewComponent

  def identifier
    @identifier ||="::Component", "").underscore.split("/").join("--")

And now in your template:

<!-- component.html -->
<div data-controller="<%= identifier %>">

Isolating CSS with postcss-modules

Our JS code is isolated by design but our CSS is still global. Hence we should care about naming, use some convention (such as BEM) or whatever.

Alternatively, we can leverage the power of modern frontend technologies such as CSS modules via postcss-modules plugin. It allows you to use local class names in your component, and takes care of generating unique names in build time. We can configure PostCSS Modules to follow our naming convention, so, we can generate the same unique class names in both JS and Ruby.

First, install the postcss-modules plugin (yarn add postcss-modules).

Then, add the following to your postcss.config.js:

module.exports = {
  plugins: {
    'postcss-modules': {
      generateScopedName: (name, filename, _css) => {
        const matches = filename.match(/\/app\/frontend\/components\/?(.*)\/index.css$/);
        // Do not transform CSS files from outside of the components folder
        if (!matches) return name;

        // identifier here is the same identifier we used for Stimulus controller (see above)
        const identifier = matches[1].replace("/", "--");

        // We also add the `c-` prefix to all components classes
        return `c-${identifier}-${name}`;
      // Do not generate *.css.json files (we don't use them)
      getJSON: () => {}
    /// other plugins

Finally, let's add a helper to our view components:

class ApplicationViewComponent

  # the same as above
  def identifier
    @identifier ||="::Component", "").underscore.split("/").join("--")

  # We also add an ability to build a class from a different component
  def class_for(name, from: identifier)

And now in your template:

<!-- example/component.html -->
<div class="<%= class_for("container") %>">
  <p class="<%= class_for("body") %>"><%= text %></p>

Assuming that you have the following index.css:

.container {
  padding: 10px;
  background: white;
  border: 1px solid #333;

.body {
  margin-top: 20px;
  font-size: 24px;

The final HTML output would be:

<div class="c-example-container">
  <p class="c-example-body">Some text</p>

I18n integration (alternative)

ViewComponent recently added (experimental) I18n support, which allows you to have isolated localization files for each component. Isolation rocks, but managing dozens of YML files spread accross the project could be tricky, especially, if you rely on some external localization tool which creates these YMLs for you.

We provide an alternative (and more classic) way of dealing with translations—namespacing. Following the convention over configuration, put translations under <locale>.view_components.<component_scope> key, for example:

      submit: "Log in"
        login: "Log in"
        logout: "Log out"

And then in your components:

<!-- login_form/component.html.erb -->
<button type="submit"><%= t(".submit") %></button>

<!-- nav/user_info/component.html.erb -->
<a href="/logout"><%= t(".logout") %></a>

If you're using ViewComponentContrib::Base, you already have translation support included. Othwerwise you must include the module yourself:

class ApplicationViewComponent < ViewComponent::Base
  include ViewComponentContrib::TranslationHelper

You can override the default namespace (view_components) and a particular component scope:

class ApplicationViewComponent < ViewComponentContrib::Base
  self.i18n_namespace = "my_components"

class SomeButton::Component < ApplicationViewComponent
  self.i18n_scope = %w[legacy button]

Hanging #initialize out to Dry

One way to improve development experience with ViewComponent is to move from imperative #initialize to something declarative. Our choice is dry-initializer.

Assuming that we have the following component:

class FlashAlert::Component < ApplicationViewComponent
  attr_reader :type, :duration, :body

  def initialize(body:, type: "success", duration: 3000)
    @body = body
    @type = type
    @duration = duration

Let's add dry-initializer to our base class:

class ApplicationViewComponent
  extend Dry::Initializer

And then refactor our FlashAlert component:

class FlashAlert::Component < ApplicationViewComponent
  option :type, default: proc { "success" }
  option :duration, default: proc { 3000 }
  option :body

Supporting .with_collection

The .with_collection method from ViewComponent expects a component class to have the "Component" suffix to correctly infer the parameter name. Since we're using a different naming convention, we need to specify the collection parameter name explicitly. For example:

class PostCard::Component < ApplicationViewComponent
  with_collection_parameter :post

  option :post

You can add this to following line to your component generator (unless it's already added): with_collection_parameter :<%= singular_name %> to always explicitly provide the collection parameter name.

Wrapped components

Sometimes we need to wrap a component into a custom HTML container (for positioning or whatever). By default, such wrapping doesn't play well with the #render? method because if we don't need a component, we don't need a wrapper.

To solve this problem, we introduce a special ViewComponentContrib::WrapperComponent class: it takes any component as the only argument and accepts a block during rendering to define a wrapping HTML. And it renders only if the inner component's #render? method returns true.

<%= render do |wrapper| %>
  <div class="col-md-auto mb-4">
    <%= wrapper.component %>
<%- end -%>

You can add a #wrapped method to your base class to simplify the code above:

class ApplicationViewComponent < ViewComponent::Base
  # adds #wrapped method
  # NOTE: Already included into ViewComponentContrib::Base
  include ViewComponentContrib::WrappedHelper

And the template looks like this now:

<%= render do |wrapper| %>
  <div class="col-md-auto mb-4">
    <%= wrapper.component %>
<%- end -%>

You can use the #wrapped method on any component inherited from ApplicationViewComponent to wrap it automatically:

ToDo list

  • Better preview tools (w/o JS deps 😉).
  • Hotwire-related extensions.


The gem is available as open source under the terms of the MIT License.