How to create custom HTML output for an existing Asciidoctor Asciidoc macro?

Question

For example, I want to add the loading="lazy" attribute to all my images e.g.:

image::myimage.jpg[]

but the default HTML

Answer 1

This is documented at: https://asciidoctor.org/docs/user-manual/#provide-custom-templates but it feels like a minimal example would be beneficial.

main.adoc

image::myimage.jpg[]

template_dir/block_image.html.erb

<%#encoding:UTF-8%> class="<%= ['imageblock',@style,role].compact * ' ' %>"<%
if (attr? :align) || (attr? :float)
%> style="<%= [("text-align: #{attr :align};" if attr? :align),("float: #{attr :float};" if attr? :float)].compact * ' ' %>"<%
end %>>
<%
if attr? :link %>
<%= (attr? :height) ? %( height="#{attr :height}") : nil %>><%
else %>
<%= (attr? :height) ? %( height="#{attr :height}") : nil %>><%
end %>
<%
if title? %>
<%= captioned_title %>
<%
end %>