Overriding built in tags

To change the behavior of existing tags, we can just override their class definitions.

For example we can look at the Template tag class definition and override the to_html method to put out different markup:

require "jsduck/tag/template"

class JsDuck::Tag::Template
  def to_html(context)
    "<p class='template-highlight'>It's a template!</p>"
  end
end

In addition to the to_html we'd also like to change the @css instance variable. We could just override the initialize method:

class JsDuck::Tag::Template
  def initialize
    @pattern = "template"
    @signature = {:long => "template", :short => "TMP"}
    @html_position = POS_TEMPLATE
    # Box with light gray background
    @css = <<-EOCSS
      .template-highlight {
        font-weight: bold;
        color: red;
      }
    EOCSS
    super
  end

  ...
end

But this way we end up duplicating a bunch of other unrelated code of which we're not at all interested. A better approach is to call the overridden method first and then apply some additional modifications on top of that:

class JsDuck::Tag::Template
  alias_method :old_initialize, :initialize

  def initialize
    old_initialize
    @css = <<-EOCSS
      .template-highlight {
        font-weight: bold;
        color: red;
      }
    EOCSS
  end

  ...
end

Here we're using alias_method to give the old initialize method another name before we override it. It's not the cleanest approach, but unless you're going to override it several times (and I see no reason to) this should be good enough.