_form.html.erb

<div id="image"></div>
<%= s3_uploader_form post: posts_path, as: "image[image_url]" do %>
  <%= file_field_tag :file, multiple: false %>
<% end %>
<script id="template-upload" type="text/x-tmpl">
<div class="upload">
  {%=o.name%}
  <div class="progress"><div class="bar" style="width: 0%"></div></div>
</div>
</script>