unpoly-rails: Ruby on Rails bindings for Unpoly

Unpoly is a backend-agnostic unobtrusive JavaScript framework. unpoly-rails gives your Ruby on Rails application some convenience candy when you are using Unpoly in your frontend.


The methods documented below are available in all controllers, views and helpers.

Detecting a fragment update

To test whether the current request is a fragment update:


To retrieve the CSS selector that is being updated:


The Unpoly frontend will expect an HTML response containing an element that matches this selector. If no such element is found, an error is shown to the user.

Server-side code is free to optimize its response by only returning HTML that matches this selector:

if up.target?('.sidebar')
  = render 'expensive_sidebar_partial'

Pushing a document title to the client

To force Unpoly to set a document title when processing the response:

up.title = 'Title from server'

This is useful when you skip rendering the <head> in an Unpoly request.

Detecting an Unpoly form validation

To test whether the current request is a form validation:


When detecting a validation request, the server is expected to validate (but not save) the form submission and render a new copy of the form with validation errors. A typical saving action should behave like this:

class UsersController < ApplicationController

  def create
    user_params = params[:user].permit(:email, :password)
    @user = User.new(user_params)
    if up.validate?
      @user.valid?  # run validations, but don't save to the database
      render 'form' # render form with error messages
    elsif @user.save?
      render 'form', status: :bad_request


Automatic redirect detection

unpoly-rails installs a before_action into all controllers which echoes the request's URL as a response header X-Up-Location and the request's HTTP method as X-Up-Method.

The Unpoly frontend requires these headers to detect redirects, which are otherwise undetectable for an AJAX client.

Automatic method detection for initial page load

unpoly-rails sets an _up_method cookie that Unpoly needs to detect the request method for the initial page load.

If the initial page was loaded with a non-GET HTTP method, Unpoly will fall back to full page loads for all actions that require pushState.

The reason for this is that some browsers remember the method of the initial page load and don't let the application change it, even with pushState. Thus, when the user reloads the page much later, an affected browser might request a POST, PUT, etc. instead of the correct method.

What you still need to do manually

Failed form submissions must return a non-200 status code

Unpoly lets you submit forms via AJAX by using the form[up-target] selector or up.submit() function.

For Unpoly to be able to detect a failed form submission, the form must be re-rendered with a non-200 HTTP status code. We recommend to use either 400 (bad request) or 422 (unprocessable entity).

To do so in Rails, pass a :status option to render:

class UsersController < ApplicationController

  def create
    user_params = params[:user].permit(:email, :password)
    @user = User.new(user_params)
    if @user.save?
      render 'form', status: :bad_request



Before you make a PR

Before you make a PR, please have some discussion about the proposed change by opening an issue on GitHub.

Running tests

  • Install Ruby 2.1.2
  • Install Bundler by running gem install bundler
  • cd into spec_app
  • Install dependencies by running bundle install
  • Run rspec

Making a new release

New versions of unpoly-rails are released as part of the Unpoly release process, which also feeds other package managers like Bower or npm.