Code snippet tested with Rails 2.3

  def index
    # ...
    if request.xhr?
      html = render_to_string(:partial => "list", :layout => false)
      respond_to do |format|
        format.html { render :text => html }
        format.json { render :json => {:html => html, ... } }
      end
    end
  end

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

• Prevents you from data breaches and liability risks
• Upgrade at your own pace
• Works with modern Rubies

Read more Show archive.org snapshot

Note: Perhaps you ran into ActionView::MissingTemplate error and this card might help. If you call render_to_string within the format.json block, Rails will only look for an index.json template, but not for an index.erb template.