モモンガでも使えるAjax（えいじゃっくす） − 投稿したコメントをリロードせずに表示しよう ref: http://qiita.com/Yama-to/items/377f8a92cf30a3ebf454

_comment.html.haml

-# 変更なし

comments_controller.rb

def create
  Comment.create(comment_params)
  @prototype = Prototype.find(params[:id])
end

create.js.erb

$('#comment_field').val('');
$('#comments').html(
  '<%= j(render partial: 'prototypes/comment', collection: @prototype.comments) %>'
);

sample.html.haml

#comments
  = render partial: 'prototypes/comment', collection: @prototype.comments
%div
  = form_for @new_comment, remote: true do |f|
    %h4 Write a comment
    = f.text_area :text, id: "comment_field"
    = f.submit :comment, class: "btn btn-primary"

show.html.haml

%div
  = render @prototype.comments
%div
  = form_for @new_comment do |f|
    %h4 Write a comment
    = f.text_area :text
    = f.submit :comment, class: "btn btn-primary"