Setting up Rails with React and Jest

React is Awesome! Rails is Awesome! Jest is awesome! Using Jest with React in Rails should be Awesome Cubed… and yet it seems so difficult.

Recently, the author was in a position where a legacy project wanted to redesign the front-end while keeping the Rails backend. The project decided to go with a React based redesign phased in, piecemeal, over time. Eventually the old JavaScript would just disappear.

The old JavaScripts had no unit testing, only some integration testing through Cucumber and Selenium. A key requirement of the new front-end was to add unit-testing to the JavaScripts, hopefully getting to a point where the team could practice some TDD (despite DHH’s proclamation that TDD is dead).

Other guides provided quite a bit of insight on the direction to take. Oliver Lance’s Rails, React, Browserify: Packaging your React components article was especially useful. However, it did not address testing. Integration tests were possible using Oliver’s setup, but Jest was unusable.

This article seeks to provide a decent setup for using React in Rails, with all Node packages, Jest test functionality, and react_ujs Rails helpers. We accomplish this using two sweet gems, react-rails and browserify-rails, and a little bit of glue.

All of the code used in this article is available on GitHub.

Basic Rails Setup

We assume a working knowledge of Rails. However, as a simple scaffolding upon which to build, we will be using the following setup.

  1. rails new rex -T

  2. Remove Turbolinks (technically optional)

    • from the Gemfile

          # Gemfile
          source ''
          gem 'rails', '4.1.8'
          gem 'sqlite3'
          gem 'sass-rails', '~> 4.0.3'
          gem 'coffee-rails', '~> 4.0.0'
          gem 'uglifier', '>= 1.3.0'
          gem 'therubyracer',  platforms: :ruby
          gem 'jquery-rails'
          gem 'jbuilder', '~> 2.0'
          gem 'spring',        group: :development
          gem 'thin'
    • from application.js

          // app/assets/javascripts/application.js
          //= require jquery
          //= require jquery_ujs
          //= require_tree .
  3. cd rex; bundle install

  4. rails generate controller pages index --no-helper --no-assets --no-controller-specs --no-view-specs

  5. Update Rails routes root to new pages#index.

    # config/routes.rb
    Rails.application.routes.draw do
      get 'pages/index'
      root to: 'pages#index'

Add in React-Rails

The best part of React-Rails is the React UJS and the view helpers. However, the stable versions of react-rails only contain react.js. Hopefully the react-rails project will correct this shortcoming in the future as react_ujs is the most valuable part of the gem. In the meantime, use the 1.0.0.pre branch directly from GitHub.

  1. Add ‘react-rails’ to the Gemfile.

    echo "gem 'react-rails', '~> 1.0.0.pre', github: 'reactjs/react-rails'" >> Gemfile
  2. bundle install

  3. Add react-rails to the application config.

    # config/application.rb
    config.react.variant      = :production
    config.react.addons       = true
  4. Setup react-rails for development mode.

    # config/environments/development.rb
    config.react.variant = :development
  5. Add React to application by adding react via two sprocket includes //= require react and //= require react_ujs. This will change in the next section, but only slightly.

    • First, create a new components.js file which will include all of our React components.

        // app/assets/javascripts/components.js
        //= require react
        //= require react_ujs
    • Then update application.js by removing the require_tree directive and including the new components.js code.

        // app/assets/javascripts/application.js
        //= require jquery
        //= require jquery_ujs
        //= require components

At this point it is possible to create React components by placing them in the components.js file and calling them with react_component 'ComponentName', {props}. in the Rails views. However, there are some limitations. First, it cannot make use of Jest for testing, though Jasmine and full integration tests should work. Second, it is not possible to require() any node packages. For example, many React applications will want to include node packages like the es6-promise or reflux packages.


The general solution for adding CommonJS and require() for React is to use a package like browserify. Fortunately, there’s a gem for that: browserify-rails. Installation is fairly straight forward.

  1. Verify that Node is installed.

  2. Add browserify-rails to the gemfile.

    echo "gem 'browserify-rails', '~>0.5'" >> Gemfile
  3. bundle install

  4. Create a package.json file.

      "name": "rex-app",
      "devDependencies": {
        "browserify": "~>6.3",
        "browserify-incremental": "^1.4.0",
        "reactify": "^0.17.1"
      "engines": {
        "node": ">=0.10.0"

    Important! Any package that needs to be require()d should be added to the devDependencies of package.json.

    Update: 2015-02-11 The browserify-rails was updated to use browserify-incremental. This means we need to add ‘browserify-incremental’ to your package.json. Trying to use browserify-rails without browserify-incremental will appear to work fine, but will throw an exception when making changes to JavaScript files and refreshing the page. Please add the following to your package.json file to work with browserify-rails 0.7.2 and above.

        "browserify-incremental": "^1.4.0"
  5. npm install

    • Note: add /node_modules to the .gitignore file if git is being used.
  6. Enable converstion of JSX to JS by adding the following param to config/application.rb

    config.browserify_rails.commandline_options = "--transform reactify --extension=\".jsx\""
  7. Create a components/ directory in app/assets/javascripts/. All React components will go in this directory.

  8. Add components.

    var DemoComponent = React.createClass({displayName: 'Demo Component',
      render: function() {
        return <div>Demo Component</div>;
    // each file will export exactly one component
    module.exports = DemoComponent;
  9. Update components.js to link required modules from the components directory.

    // note that this is a global assignment, it will be discussed further below
    DemoComponent = require('./components/DemoComponent');
  10. Add the demo component into our view.

    <%= react_component 'DemoComponent', {} %>

This setup gives us require(). However, there are some things to note. First, do not require('react') via CommonJS require(). React is being loaded globaly by react-rails via the sprocket //= require react directive. A second inclusion will cause React to throw errors. Second, each and every single component that should be available globally needs to be require()d in components.js. CommonJS does not have an equivalent to the sprocket //= require_tree directive.

Fixing Browserify/React-Rails

Problem, require('react') is necessary if we want to use Jest. The solution so far provides require() for other libraries, but not require('react'). So, how to get this crucial last requirement. Presently, the only workable solution is to ignore the react.js asset provided by react-rails and use the Node version instead.

  1. Replace //= require react with require('react') in component.js

    //= require_self
    //= require react_ujs
    React = require('react');
    // put components here
    DemoComponent = require('./components/DemoComponent');

    //= require_self is called before //= require react_ujs. This allows react.js to be loaded from node modules instead of react-rails.

  2. Update package.json with the following in devDependencies:

    "react": "^0.12.0",
    "react-tools": "^0.12.1"
  3. Run npm install again.

  4. Add var React = require('react'); to your top of each of your components. For example:

    var React = require('react');
    var DemoComponent = React.createClass({displayName: 'Demo Component',
      render: function() {
        return <div>Demo Component</div>;
    module.exports = DemoComponent;

Now we can require('react'), export the component via module.exports, and inject components with react_component Rails view helpers.


We can finally get going with Jest. Jest is based on Jasmine and used by Facebook to test React. It automatically mocks out all modules except those being tested, it can run tests in parallel, and it runs in a fake DOM implementation. Bottom line, Jest is awesome.

However, Jest really wants a CommonJS structure where everything is included via require(). That is why we had to go through all the trouble in the previous sections. Fortunately, now that the hard work is done, making Jest work is relatively easy. It requires updating package.json, creating a new directory, and adding a couple of script files.

  1. Create a directory for the tests in app/assets/javascripts/components/__tests__.

    Note that Rails generally puts tests in a test/ or spec/ directory. However, it is easier to put Jest tests in a __tests__ directory under the actual components. Otherwise, the test require() statements end up with lots of brittle, ugly ../../../app/assets/javascripts/components/[component]s.

    Placing the tests here has one slight complication though. Sprocket’s //= require_tree will include the tests as part of the build. This should not be an issue as the components/ directory should not be part of any //= require_tree directive anyway, as that also would break the CommonJS structure we use.

  2. Create a file app/assets/components/javascripts/__tests__/preprocessor.js to convert any JSX to JS (remember that browserify-rails does this via reactify when running via Rails).

    var ReactTools = require('react-tools');
    module.exports = {
      process: function(src) {
        return ReactTools.transform(src);
  3. Add and configure Jest in the package.json

    "devDependencies": {
      "jest-cli": "^0.5.4",
    "scripts": {
      "test": "node ./node_modules/jest-cli/bin/jest.js"
    "jest": {
      "rootDir": "./app/assets/javascripts/components",
      "scriptPreprocessor": "<rootDir>/__tests__/preprocessor.js",
      "moduleFileExtensions": [ "js", "jsx"],
      "unmockedModulePathPatterns": [
      "testFileExtensions": ["js", "jsx"],
      "testPathIgnorePatterns": [ "preprocessor.js" ]

* `rootDir` points to the components directory (Jest will automatically load the __tests__ path by default).
* `scriptPreprocessor` points to our JSX preprocessor script.
* `umockedModulePathPatterns` tells Jest not to mock out React, which we need for our components to work.
* `testPathIgnorePatterns` tells Jest to ignore our JSX preprocessor. Placing `preprocessor.js` in a different directory would eliminate the need for this directive. However, this feels cleaner.

Update: 2015-09-21 The original version of this post used "jest-cli": "^0.2.0", which began producing errors with certain versions of Node. The version has been updated to "jest-cli": "^0.5.4", which solves that issue. However due a decision by the JSDOM package to support io.js rather than node when they were separated, this requires version using Node v4.0.0 or higher. When it comed to Jest, your options are:

  • Jest 0.4 with Node 0.10
  • Jest 0.5 with io.js 2+ or Node v4.0+
  • In the future it will be Jest 0.6+ with Node 4.0+ only.

You can read more about this in this github issue.

  1. npm install

  2. Create a test for our demo component.

    // app/assets/javascripts/components/__tests__/DemoComponent-test.jsx

    describe('DemoComponent', function() {
      it('should tell use it is a demo component', function() {
        var React = require('react/addons');
        var TestUtils = React.addons.TestUtils;
        var DemoComponent = require('../DemoComponent');
        var demoComponent = TestUtils.renderIntoDocument(<DemoComponent/>);
            expect(demoComponent.getDOMNode().textContent).toBe('Demo Component');
  1. Run tests with npm test.

Now it is possible to run Jest based tests, require() CommonJS packages, and inject React via Rails views.

Gotchas with jQuery and other Gem-based Assets

The basic Rails application uses the jquery-rails gem. jquery-rails has the same problem with require('jquery') that react-rails has with require('react'). This will be a problem with any application that adds assets via gems and tries to use both //= require and require() for that asset. Fortunately, jQuery is resilient to multiple includes, so the only real concern is bloat.

The maintainers of browserify-rails know about the problem. Hopefully, a solution is implemented soon. In the mean time, one potential solution is to remove the jquery-rails gem, //= require jquery and //= require jquery_ujs. Another solution, if your project needs these gems, is to add jQuery to application.js the way react.js is added to components.js.

//= require_self
//= require jquery_ujs
//= components

$ = jQuery = require('jquery');

Then add jQuery to the devDependencies of package.json. (Remember that all require()d packages must be in package.json and npm installed).

"devDependencies": {
    "jquery": "^2.1.1"


We have setup Rails to work with React, Node packages, and Jest. To use this setup, simply add React components to the app/assets/javascript/components/ directory and put any global components that the react_component view helper might need in app/assets/javascripts/components.js. Tests are simple Jest tests in the app/assets/javascripts/components/__tests/ directory. Rspec/Cucumber integration tests should work as expected too.

Hopefully, this article has been useful to help setup a foundation for using React and Jest in your Rails application.