application_helper.rb

  def handlebars_js(name, opts = {}, &block)
    inner = capture(&block).gsub(/\s*\n\s*/, " ")
    concat raw "window._templates['#{name}'] = #{inner.to_json};\n"
    nil
  end

templates.js.haml

window._templates = {};

- handlebars_js "post" do
  %h1
    =link_to "{{title}}", "/stories/{{id}}-{{slug}}/", :target => "_top"
  - link_to "/stories/{{id}}-{{slug}}/", :target => "_top" do
    %img.thumb{:src => "{{images.i300x200}}"}
  .body
    .excerpt
      {{{content.excerpt}}}
    %footer
      %time {{post_date}}
      by {{author}}
      %span.shares {{shares.total}} shares

:plain
  window._template_cache = {};
  for(var name in window._templates) {
    if(window._templates.hasOwnProperty(name)) {
      window._template_cache[name] = Handlebars.compile(window._templates[name]);
    }
  }

view.html.haml

=javascript_include_tag "/whatever/templates.js"

#anchor
:javascript
  $("#anchor").html _template_cache["post"]({title: "Yay!", content: {excerpt: "More yay!"}});