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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.

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.

Adding tags

You can add a custom tag using the Lookbook.define_tag method when you configure your Lookbook installation:

Lookbook.define_tag(<name>, <arg_names?>)

A unique name for the tag

Type: Symbol

Array of positional argument names to match to values when parsing the tag body contents.

Type: Array

Basic example

In the following example we will create a @status tag that will allow a workflow status ‘label’ to be applied to each preview. For example:

@status wip    # work in progress
@status ready  # can be used

The @status tag only expects a single argument (current_status), so we can define the tag as follows:

# config/application.rb
Lookbook.define_tag(:status, [:current_status])

All parsed argument values can be then accessed as properties of the tag object when using in templates:

<p>Current status: <%= tag.current_status # 'wip' %></p>

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 options can be specified.

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

The @status example above doesn’t need any changes in order to support accepting options - the parser will automatically handle them if they are found in the tag body.

@status wip { display_style: badge }

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

Current status:
<% if tag.opts[:display_style] == "badge" %>
  <span class="badge">
    <%= tag.current_status %>
<% else %>
  <%= tag.current_status %>
<% end %>

Using 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.define_tag method when adding a new tag.

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

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

See below for details on available tag object properties and methods.

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

Accessing tag data in panel templates

An array of related tags is available via the .tags method on both preview and example objects in panel templates:

<ul id="todo-list">
  <% preview.tags(:todo).each do |todo| %>
    <li><%= todo.task %></li>
  <% end %>

<p>Preview example status: "<%= example.tag(:status).current_status %>"</p>

See the Preview and PreviewExample API docs for more details.