Components Basics

In order to create a new component you need to define a module and use one of the available component types:

  • Surface.Component - A stateless component.
  • Surface.LiveComponent - A live stateful component.
  • Surface.LiveView - A wrapper component around Phoenix.LiveView.
  • Surface.MacroComponent - A low-level component which is responsible for translating its own content at compile time.

Components instances can be injected in a template using the same notation as any other HTML tag.

Hello, I'm a component! 
# Defining the component

defmodule Hello do
  use Surface.Component

  def render(assigns) do
    ~F"""
    Hello, I'm a component!
    """
  end
end

# Using the component

defmodule Example do
  use Surface.Component

  def render(assigns) do
    ~F"""
    <Hello />
    """
  end
end

Colocated templates

In case you want to isolate all templating code into a separate file, you can create a .sface file using the same base name in the same directory of the related component or liveview. For instance:

components
├── example.ex
├── example.sface
├── hello.ex
└── hello.sface
...

This way you can remove the implemented render/1 altogether. Any defined assign or function will be available in the new template.

Note: Unlike EEX templates, which can be used with any kind of text file, Surface's templates already extend HTML. Therefore, they are named simply as *.sface instead of *.html.sface.

Using aliases

Since a component is just a module, it can injected using either its full name or a valid alias.

Using full module name:

<MyProject.Components.MyButton>
<MyProject.Components.MyLink>

Using aliases:

alias MyProject.Components.MyButton
alias MyProject.Components.MyLink, as: Link

def render(assigns) do
  ~F"""
  <MyButton>Ok</MyButton>
  ...
  <Link>
    ...
  </Link>
  """
end

The component API

Surface provides built-in functions that should be used to declare the essential building blocks of any component:

  • prop - Defines a property for the component.

  • data - Defines a data assign for a stateful LiveComponent or LiveView. The set of all data assigns represents the state of the component/view.

  • slot - Defines a placeholder (slot) that can be filled up with custom content.

All values declared using any of the above functions will be merged into the components assigns and will be available inside the template using the @ prefix.

Having everything explicitly declared brings a lot of benefits since all information provided can be used later for introspection allowing Surface to provide:

  • Syntactic sugar on attributes definition - e.g. CSS style classes.
  • Improved API for events - automatically setting phx-target.
  • Compile-time checking - validations of required properties, incompatible slots, etc.
  • Integration with editor/tools - for warnings/errors, syntax highlighting, jump-to-definition, auto-completion and more.
  • Docs generation - see the Button component below.

Let's take a look at how a component can be defined using Surface's API.

defmodule Button do
  use Surface.Component

  @doc "The type (color) of the button"
  prop type, :string, values: ["primary", "success", "info"]

  @doc "The Button is expanded (full-width)"
  prop expanded, :boolean, default: false

  @doc "Triggers on click"
  prop click, :event

  @doc "Triggers on focus"
  prop focus, :event

  @doc "The content of the button"
  slot default, required: true

  ...
end

The public API of the Button above can be automatically generated, including all information about properties, slots and events, divided by group in each individual tab as follows:

Name Description Type Values Default
type The type (color) of the button.

 		:string primary, success, info —
expanded The Button is expanded (full-width).

 		:boolean — false

Public vs private

Using property and slot defines the public API of the component as their values are initialized outside the component. Assigns declared as data are considered private since they can only be accessed inside the component's scope.

It's important to keep that distinction in mind when designing a new component. Remember that users need to be able to easily identify the public interface so they can properly interact with the component. The recommendation is to have everything explicitly declared and well documented using Surface's component API.