Extending Lookbook / Custom Tags

Custom Tags

It is possible to define new tags for use when annotating preview files.

Tag data can then be accessed in custom inspector panels and so can be used to build bespoke functionality that would otherwise not be natively supported by Lookbook.

Adding a custom tag

To register a custom tag use the Lookbook.add_tag method when when you configure your Lookbook installation:

Lookbook. add_tag (name, args = nil)


name Symbol,String

Tag name

args Array<Symbol>

Array of argument names

For example, an @design tag to reference design files could be implemented as follows:

# config/application.rb
Lookbook.add_tag(:design, [:tool_name, :design_file_url])

This could then be used to annotate preview classes (or scenario methods):

# @design figma https://share.figma.com/my-org/button-component
class ButtonComponentPreview < Lookbook::Preview
  def default
    render ButtonComponent.new do
      "Click me"

And accessed within a custom inspector panel template:

<h1>Reference designs</h1>
  <% preview.tags(:design).each do |tag| %>
      <a href="<%= tag.design_file_url %>">
        <%= tag.tool_name %>
  <% end %>

Tag structure

Lookbook tags take the following form:

@tag_name <tag_body>

The <tag_body> is a string of arbitrary free text which can be anything you want.

However in practice most tags expect this text to contain one or more space-separated positional arguments, optionally followed by a set of options:

@tag_name <arg_1> <arg_2> ... <arg_x> <opts?>

The @param tag provides a good example of this in action:

@param rating select { choices: [Bad, Good, Average] }

In the above example the @param tag body will be parsed to extract the following information:

  name value type
1st argument param_name rating String
2nd argument field_type select String
rest of tag body options { choices: ["Bad", "Good", "Average"] } Hash

Because tag arguments are space-separated, argument values that need to contain a space must be surrounded by double quotes:

@tag_name first_arg "second value" third

Tag body parsing

By default, Lookbook will attempt to parse the tag body into a set of argument values and options. To make this possible an array of argument names (in the order which the values will appear in the tag body) needs be provided when defining a new tag.

If your desired custom tag structure does not fit the standard format outlined above, then it is also possible to provide your own custom parser to take full control of the process.

Tag options

An (optional!) set of options can be provided at the end of the tag body content.

Options can provided inline (as a YAML hash), imported from a JSON/YAML file or generated dynamically. Custom tag options are handled in exactly the same way as @param tag options so check out the param options documentation for more detals on how they can be specified.

The example below will use the simplest option - an inline, YAML-formatted hash.

# @design figma https://share.figma.com/my-org/button-component { status: wip }

The provided options hash can be accessed via the .opts property on tag objects:

<a href="<%= tag.design_file_url %>">
  <%= tag.tool_name %>
  <% if tag.opts.status == "wip" %>
    <strong>IN PROGRESS</strong>
  <% end %>

Custom parsing logic

In some cases you may want to implement you own tag body parsing logic, to either replace or augment the standard parsing behavior.

You can do this by providing a block to the Lookbook.add_tag method when adding a new tag.

The block will receive a tag object as its only argument - the parser can access tag information from this and set arbitrary properties on this object for later use in templates.

Lookbook.add_tag(:new_tag) do |tag|
  # custom parser logic here...

Keywords example

In this example, we will define a @keywords tag which allows for specifying a list of keywords in comma-separated list:

@keywords marketing, email, webinar

The standard parsing behaviour would not work here - it would attempt to parse each keyword as an argument value.

Instead we can use some custom parsing logic to generate an array from the comma-separated list, and store it on the tag object for later reference.

Lookbook.add_tag(:keywords) do |tag|
  tag.keywords = tag.tag_body.split(",").map(&:strip)
The keywords for this preview are: <%= tag.keywords.join(" | ") %>

User Guide

Extending Lookbook