foo.haml

:template{id: "foo"}
  .this
    .that.somethingelse
      %h1 Title
    .body
      some text {{foo}}

html.html

<script type="text/javascript" id="foo">
  <div class="this">
    <div class="that somethingelse">
      <h1>Title</h1>
    </div>
    <div class="body">
      som text {{foo}}
    </div>
  </div>
</script>