application.dryml

<def tag="js-wrapper" attrs="convert">
  <set-scoped vals="&[]">
    <do param="default" />
    <% if convert %>
      <%= "[#{scope.vals.*.inspect.join(', ')}]" %>
    <% else %>
      <% scope.retval = scope.vals %>
    <% end %>
  </set-scoped>
</def>

<def tag="hash-param" attrs="key">
  <set-scoped retval="">
    <% value = parameters.default %>
    <% value = scope.retval if value.blank? %>
    <% scope.vals << Hash[key, value] %>
  </set-scoped>
</def>

<def tag="array-param">
  <set-scoped retval="">
    <% value = parameters.default %>
    <% value = scope.retval if value.blank? %>
    <% scope.vals << value %>
  </set-scoped>
</def>

usage.dryml

<js-wrapper convert>
  <array-param>Foo</array-param>
  <hash-param key="Bar">Baz</hash-param>
  <array-param>Blah</array-param>
  <hash-param key="more">
    <js-wrapper>
      <array-param>Foo2</array-param>
      <hash-param key="Bar2">Baz2</hash-param>
      <array-param>
        <js-wrapper>
          <hash-param key="Bar3">Baz3</hash-param>
          <array-param>Blah4</array-param>
        </js-wrapper>
      </array-param>
    </js-wrapper>
  </hash-param>
</js-wrapper>


Result:
["Foo", {"Bar"=>"Baz"}, "Blah", {"more"=>["Foo2", {"Bar2"=>"Baz2"}, [{"Bar3"=>"Baz3"}, "Blah4"]]}]