Elemental Components

Simple view components for Rails 5.1+, designed to go well with elemental_styleguide. The two together are inspired by the works of Brad Frost and by the thoughts behind Lonely Planet's style guide Rizzo.

Installation

Add this line to your application's Gemfile:

gem "elemental_components"

And then execute:

$ bundle

Components

The examples provided here will use the BEM naming conventions.

Components live in app/components. Generate a component by executing:

$ bin/rails g elemental_components:component alert

This will create the following files:

app/
  components/
    alert/
      _alert.html.erb
      alert.css
      alert.js
    alert_component.rb

The generator also takes --skip-css and --skip-js options.

Let's add some markup and CSS:

<% # app/components/alert/_alert.html.erb %>

<div class="alert alert--primary" role="alert">
  Message
</div>

/* app/components/alert/alert.css */

.alert {
  padding: 1rem;
}

.alert--primary {
  background: blue;
}

.alert--success {
  background: green;
}

.alert--danger {
  background: red;
}

This component can now be rendered using the component helper:

<%= component "alert" %>

Assets

In order to require assets such as CSS, either require them manually in the manifest, e.g. application.css:

/*
 *= require alert/alert
 */

Or require components, which will in turn require the assets for all components:

/*
 *= require elemental_components
 */

Attributes and content blocks

There are two ways of passing data to components: attributes and content blocks. Attributes are useful for data such as ids, modifiers and data structures (models etc). Content blocks are useful when you need to inject HTML content into components.

Let's define some attributes for the component we just created:

# app/components/alert_component.rb %>

class AlertComponent < ElementalComponents::Component
  attribute :context
  attribute :message
end

<% # app/components/alert/_alert.html.erb %>

<div class="alert alert--<%= alert.context %>" role="alert">
  <%= alert.message %>
</div>

<%= component "alert", message: "Something went right!", context: "success" %>
<%= component "alert", message: "Something went wrong!", context: "danger" %>

To inject some text or HTML content into our component we can print the component .content method in our template, and populate it by passing a content block to the component helper:

<% # app/components/alert/_alert.html.erb %>

<div class="alert alert--<%= alert.context %>" role="alert">
  <%= alert.content %>
</div>

<%= component "alert", context: "success" do %>
  <em>Something</em> went right!
<% end %>

Another good use case for attributes is when you have a component backed by a model:

# app/components/comment_component.rb %>

class CommentComponent < ElementalComponents::Component
  attribute :comment

  delegate :id,
           :author,
           :body, to: :comment
end

<% # app/components/comment/_comment.html.erb %>

<div id="comment-<%= comment.id %>" class="comment">
  <div class="comment__author">
    <%= link_to comment.author.name, author_path(comment.author) %>
  </div>
  <div class="comment__body">
    <%= comment.body %>
  </div>
</div>

<% comments.each do |comment| %>
  <%= component "comment", comment: comment %>
<% end %>

Attribute defaults

Attributes can have default values:

# app/components/alert_component.rb %>

class AlertComponent < ElementalComponents::Component
  attribute :message
  attribute :context, default: "primary"
end

Attribute overrides

It's easy to override an attribute with additional logic:

# app/components/alert_component.rb %>

class AlertComponent < ElementalComponents::Component
  attribute :message
  attribute :context, default: "primary"

  def message
    @message.upcase if context == "danger"
  end
end

Attribute validation

To ensure your components get initialized properly you can use ActiveModel::Validations in your elements or components:

# app/components/alert_component.rb %>

class AlertComponent < ElementalComponents::Component
  attribute :label

  validates :label, presence: true
end

Your validations will be executed during the components initialization and raise an ActiveModel::ValidationError if any validation fails.

Elements

Attributes and blocks are great for simple components or components backed by a data structure, such as a model. Other components are more generic in nature and can be used in a variety of contexts. Often they consist of multiple parts or elements, that sometimes repeat, and sometimes need their own modifiers.

Take a card component. In React, a common approach is to create subcomponents:

<Card flush={true}>
  <CardHeader centered={true}>
    Header
  </CardHeader>
  <CardSection size="large">
    Section 1
  </CardSection>
  <CardSection size="small">
    Section 2
  </CardSection>
  <CardFooter>
    Footer
  </CardFooter>
</Card>

There are two problems with this approach:

1. The card header, section and footer have no standalone meaning, yet we treat them as standalone components. This means a CardHeader could be placed outside of a Card.
2. We lose control of the structure of the elements. A CardHeader can be placed below, or inside a CardFooter.

Using this gem, the same component can be written like this:

# app/components/card_component.rb %>

class CardComponent < ElementalComponents::Component
  attribute :flush, default: false

  element :header do
    attribute :centered, default: false
  end

  element :section, multiple: true do
    attribute :size
  end

  element :footer
end

<% # app/components/card/_card.html.erb %>

<div class="card <%= "card--flush" if card.flush %>">
  <% if card.header.content? %>
    <div class="card__header <%= "card__header--centered" if card.header.centered %>">
      <%= card.header.content %>
    </div>
  <% end%>
  <% card.sections.each do |section| %>
    <div class="card__section <%= "card__section--#{section.size}" %>">
      <%= section.content %>
    </div>
  <% end %>
  <% if card.footer.content? %>
    <div class="card__footer">
      <%= card.footer.content %>
    </div>
  <% end %>
</div>

Elements can be thought of as isolated subcomponents, and they are defined on the component. Passing multiple: true makes it a repeating element, and passing a block lets us declare attributes on our elements, in the same way we declare attributes on components.

In order to populate them with data, we pass a block to the component helper, which yields the component, which lets us set attributes and content blocks on the element in the same way we do for components:

<%= component "card", flush: true do |c| %>
  <% c.header centered: true do %>
    Header
  <% end %>
  <% c.section size: "large" do %>
    Section 1
  <% end %>
  <% c.section size: "large" do %>
    Section 2
  <% end %>
  <% c.footer do %>
    Footer
  <% end %>
<% end %>

Multiple calls to a repeating element, such as section in the example above, will append each section to an array.

Another good use case is a navigation component:

# app/components/navigation_component.rb %>

class NavigationComponent < ElementalComponents::Component
  element :items, multiple: true do
    attribute :label
    attribute :url
    attribute :active, default: false
  end
end

<%= component "navigation" do |c| %>
  <% c.item label: "Home", url: root_path, active: true %>
  <% c.item label: "Explore" url: explore_path %>
<% end %>

An alternative here is to pass a data structure to the component as an attribute, if no HTML needs to be injected when rendering the component:

<%= component "navigation", items: items %>

Elements can have validations, too:

class NavigationComponent < ElementalComponents::Component
  element :items, multiple: true do
    attribute :label
    attribute :url
    attribute :active, default: false

    validates :label, presence: true
    validates :url, presence: true
  end
end

Elements can also be nested, although it is recommended to keep nesting to a minimum:

# app/components/card_component.rb %>

class CardComponent < ElementalComponents::Component
  ...

  element :section, multiple: true do
    attribute :size

    element :header
    element :footer
  end
end

Helper methods

In addition to declaring attributes and elements, it is also possible to declare helper methods. This is useful if you prefer to keep logic out of your templates. Let's extract the modifier logic from the card component template:

# app/components/card_component.rb %>

class CardComponent < ElementalComponents::Component
  ...

  def css_classes
    css_classes = ["card"]
    css_classes << "card--flush" if flush
    css_classes.join(" ")
  end
end

<% # app/components/card/_card.html.erb %>

<%= content_tag :div, class: card.css_classes do %>
  ...
<% end %>

It's even possible to declare helpers on elements:

# app/components/card_component.rb %>

class CardComponent < ElementalComponents::Component
  ...

  element :section, multiple: true do
    attribute :size

    def css_classes
      css_classes = ["card__section"]
      css_classes << "card__section--#{size}" if size
      css_classes.join(" ")
    end
  end
end

<% # app/components/card/_card.html.erb %>

<%= content_tag :div, class: card.css_classes do %>
  ...
  <%= content_tag :div, class: section.css_classes do %>
    <%= section %>
  <% end %>
  ...
<% end %>

Helper methods can also make use of the @view instance variable in order to call Rails helpers such as link_to or content_tag.

Rendering components without a partial

For some small components, such as buttons, it might make sense to skip the partial altogether, in order to speed up rendering. This can be done by overriding render on the component:

# app/components/button_component.rb %>

class ButtonComponent < ElementalComponents::Component
  attribute :label
  attribute :url
  attribute :context

  def render
    @view.link_to label, url, class: css_classes
  end

  def css_classes
    css_classes = "button"
    css_classes << "button--#{context}" if context
    css_classes.join(" ")
  end
end

<%= component "button", label: "Sign up", url: sign_up_path, context: "primary" %>
<%= component "button", label: "Sign in", url: sign_in_path %>

Namespaced components

Components can be nested under a namespace. This is useful if you want to practice things like Atomic Design, BEMIT or any other component classification scheme. In order to create a namespaced component, stick it in a folder and wrap the class in a module:

module Objects
  class MediaObject < ElementalComponents::Component; end
end

Then call it from a template like so:

<%= component "objects/media_object" %>

Acknowledgements

This library, together with elemental_styleguide, was inspired by the writings of Brad Frost on atomic design and living style guides, and Rizzo, the Lonely Planet style guide. Other inspirations were:

• Catalog - style guide for React
• Storybook - style guide for React
• React Styleguidist - style guide for React
• Cells - view components for Ruby
• Komponent - view components for Ruby

For a list of real world style guides, check out http://styleguides.io.