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Helpers

Helpers are Ruby methods you can provide to Tilt-based templates (ERB, Slim, etc.) to transform data or output new content in various ways.

Example:

class Helpers < SiteBuilder
  def build
    helper "cache_busting_url" do |url|
      "http://www.example.com/#{url}?#{Time.now.to_i}"
    end
  end
end
<%= cache_busting_url "mydynamicfile.js" %>

outputs:

http://www.example.com/mydynamicfile.js?1586194585

Supporting Arguments

You can accept multiple arguments to your helper by simply adding them to your block or method, and optional ones are simply specified with a default value (perhaps nil or false). For example:

def Helpers < SiteBuilder
  def build
    helper "multiply_and_optionally_add" do |input, multiply_by, add_by = nil|
      value = input * multiply_by
      add_by ? value + add_by : value
    end
  end
end

Then just use it like this:

5 times 10 equals <%= multiply_and_optionally_add 5, 10 %>

  output: 5 times 10 equals 50

5 times 10 plus 3 equals <%= multiply_and_optionally_add 5, 10, 3 %>

  output: 5 times 10 plus 3 equals 53

Using Instance Methods

As with other parts of the Builder API, you can also use an instance method to register your helper:

def Helpers < SiteBuilder
  def build
    helper "cache_busting_url", :bust_it
  end

  def bust_it(url)
    "http://www.example.com/#{url}?#{Time.now.to_i}"
  end
end

Helper Execution Scope

By default, the code within the helper block or method is executed within the scope of the builder object. This means you will not have access to other helpers you may expecting to call. For example, if you want to call slugify from your helper, it will cause an error.

To remedy this, simply pass the helpers_scope: true argument when defining a helper block. Then you can call other helpers as part of your code block (but not methods within your builder).

def Helpers < SiteBuilder
  def build
    helper "slugify_and_upcase", helpers_scope: true do |url|
      slugify(url).upcase
    end
  end
end

When using the helpers scope, you have access to two variables: site and view. site is of course an instance of Bridgetown::Site, and view will be a subclassed instance of Bridgetown::RubyTemplateView which reflects the current template engine in use. For example, it will be Bridgetown::ERBView for ERB templates. This gives you access to engine-specific view methods such as partial, as well as any other custom methods that may have been defined for the view to use.

Using the Capture Helper

Within the helpers scope, you can “capture” the contents of a block and use that text inside your helper. Optionally, you can pass an object to the block itself from your helper. For example:

def Helpers < SiteBuilder
  def build
    helper "capture_and_upcase", helpers_scope: true do |&block|
      label = "upcased"
      view.capture(label, &block).upcase
    end
  end
end

Now just call that helper in your template and use the label argument:

<%= capture_and_upcase do |label| %>
  I have been <%= label %>!
<% end %>

  output: I HAVE BEEN UPCASED!

Helpers vs. Filters vs. Tags

Filters and tags are aspects of the Liquid template engine which comes installed by default. The behavior of both filters and tags are roughly analogous to helpers in Tilt-based templates. Specialized Bridgetown filters are also made available as helpers, as are a few tags such as webpack_path.

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