Initializer to override default field with errors (rails 5.0.1)

_error_messages.html.erb

<!-- path: views/layouts/ -->

<% if object.errors.any? %>
  <% object.errors.full_messages.each do |msg| %>
    <%=
      content_tag :div, :id => "has_errors", :style => "padding:3px; margin:0 20vw; background-color:rgba(246, 138, 138, 0.7); border:solid rgba(246, 138, 138, 1) 1px; border-radius:12px; text-align:center;" do
      concat(content_tag :p, msg)
      end
    -%>
  <% end %>
  <script type="text/javascript">
    <%#
      # this:
      # window.onload = scrollToError;
      # function scrollToError(){ window.location.hash = '#has_errors'; };
      # or: 
    %>
    window.onload = scrollToMiddle("#has_errors");
    function scrollToMiddle(id) {
      var elem_position = $(id).offset().top;
      var window_height = $(window).height();
      var y = elem_position - window_height/2;
      
      window.scrollTo(0,y);
    }
  </script>
<% end %>

field_with_errors.rb

module ActiveModel::Conversion
  attr_accessor :skip_field_error_wrapper
end # to skip additional class-wrapper on error

# usage:
# @user.skip_field_error_wrapper = true
# form_for(@user) do |f|...

ActionView::Base.field_error_proc = Proc.new do |html_tag, instance|
  class_attr_index = html_tag.index('class="')
  first_tag_end_index = html_tag.index('>')

  if class_attr_index.nil? || first_tag_end_index > class_attr_index
    html_tag.insert(first_tag_end_index, ' class="field_error"')
  elsif instance.object && instance.object.skip_field_error_wrapper
    html_tag.html_safe
  else
    html_tag.insert(class_attr_index + 7, 'field_error ')
  end
end

# compilation from http://stackoverflow.com/questions/5267998/rails-3-field-with-errors-wrapper-changes-the-page-appearance-how-to-avoid-t

form.html.erb

<!-- examplery form -->
<% content_for :form do %>
  <%= form_for(something) do |f| %>
    <%= render 'layouts/error_messages', object: f.object -%>
  <% end %>
<% end %>