Building your first component in Phlex

Let’s start by building a simple Card component. A Card is a presentational component, it doesn’t really have any behavior. So it’s going to be mostly for abstracting away the CSS classes and specific markup. We’ll use simple classes in our example, but you could imagine if you were using a utility based CSS framework like Tailwind that you would be abstracting away a lot more.

# app/components/card.rb
class Components::Card < Phlex::HTML
  def view_template(&)
    div(class: "card", &)
  end
end

Not the most exciting component, but it’s a start. We can use it like this:

view.rb

class View < Phlex::HTML
  def view_template
    render Card.new do
      p { "Card content" }
    end
  end
end

output

<div class="card">
  <p>Card content</p>
</div>

This is nice, but some of our cards will need a header section that has a title. Let’s keep adding to our Card component so that it can have an optional header:

class Card < Phlex::HTML
  def view_template(&)
    div(class: "card", &)
  end

  def header(&) 
    div(class: "card-header", &)
  end

  def title(&) 
    h2(class: "card-title", &)
  end
end

We’ve added header and title methods to our Card component. Now when we render a card, we can use the block argument, which will be the instance of our Card, and call our new methods:

view.rb

class View < Phlex::HTML
  def view_template
    render Card.new do
    render Card.new do |c| 
      c.header do
        c.title { "Card Title" }
      end
      p { "Card content" }
    end
  end
end

output

<div class="card">
  <div class="card-header">
    <h2 class="card-title">Card Title</h2>
  </div>
  <p>Card content</p>
</div>

Ok, this is starting to look a bit better. But we also need a way to add an action button to our card. This will need a bit more flexibility than just changing the content of the button. Let’s see what that looks like:

class Card < Phlex::HTML
  def view_template(&)
    div(class: "card", &)
  end

  def header(&)
    div(class: "card-header", &)
  end

  def title(&)
    h2(class: "card-title", &)
  end

  def action(**, &) 
    a(class: "card-action", **, &)
  end
end

This will let us pass in attributes to the action button.

view.rb

class View < Phlex::HTML
  def view_template
    render Card.new do |c|
      c.header do
        c.title { "Card Title" }
      end
      p { "Card content" }
      c.action(href: "/") { "Action" }
    end
  end
end

output

<div class="card">
  <div class="card-header">
    <h2 class="card-title">Card Title</h2>
  </div>
  <p>Card content</p>
  <a class="card-action" href="/">Action</a>
</div>

This seems like it’s working, but we actually have a bit of a problem. We can’t specify a class for our action button without overriding the class provided in the action method. Any custom class or classes we provide will clobber the default card-action class. Phlex provides a helper method to help us deal with this situation called mix. It mixes attributes together, and is aware of token lists. Let’s update our action method to use mix:

def action(**attributes, &)
  a(**mix(class: "card-action", attributes), &)
end

Now if we specify a custom class when we call our action method, it will be added to the class list instead of overriding it.

view.rb

class View < Phlex::HTML
  def view_template
    render Card.new do |c|
      c.header do
        c.title { "Card Title" }
        c.action(class: "custom-class") { "Action" }
      end
      p { "Card content" }
    end
  end
end

output

<div class="card">
  <div class="card-header">
    <h2 class="card-title">Card Title</h2>
    <a class="card-action custom-class" href="/">Action</a>
  </div>
  <p>Card content</p>
</div>