AjaxErrorRenderer

AjaxErrorRenderer is a validation error renderer for ajax request.

If you use turbolinks and form_with, you may need SJR(Server-generated JavaScript Responses) on validation errors. But it's a pain to add similar SJR code with every forms. AjaxErrorRenderer gives you render_ajax_error method to remove duplicated SJR.

Add this line to your application's Gemfile:

gem 'ajax_error_renderer'

And then execute:

$ bundle

First, include AjaxErrorRenderer in your controller like following.

class ApplicationController < ActionController::Base
  include AjaxErrorRenderer
end

Then you can use render_ajax_error method like following.

class UsersController < ApplicationController
  def new
    @user = User.new
  end

  def create
    @user = User.new(params.require(:user).permit(:name))
    if @user.save
      redirect_to users_path, notice: 'You created a user successfully!'
    else
      render_ajax_error model: @user
    end
  end
end

So error messages display within #error by default.

<%= form_with(model: @user) do |form| %>
  <div id="error">
    <%# Error Messages display here! %>
  </div>

  <div class="field">
    <%= form.label :name %>
    <%= form.text_field :name %>
  </div>

  <div class="actions">
    <%= form.submit %>
  </div>
<% end %>

If you want to display the messages in other place, you can do it by passing location option to render_ajax_error with css like following.

render_ajax_error model: @user, location: '.error_messages'

If you have a large form, users can miss validation error messages because the messages display above user screen. To solve the problem, render_ajax_error method has move option to scroll to error messages. It defaults to true.

If you won't scroll, you can write like following.

render_ajax_error model: @user, move: false

You can create custome template with a generator like following.

./bin/rails g ajax_error_renderer:view

This generator command generates app/views/ajax_errors/_error.html.erb, and you can customize it freely.

To use another templates, you can use template argument.

render_ajax_error model: @user, template: 'critical_error'

Template app/views/ajax_errors/_critical_error.html.erb will use.

The gem is available as open source under the terms of the MIT License.