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You are looking at the 2.3 stable branch. This branch is for maintaining the prebundled 15.6 ReactJS with Addons. Gem version 2.4.x onwards and master will no longer have React Addons.

If you need to make changes for the prebundled react, see the migration docs here: https://reactjs.org/blog/2016/11/16/react-v15.4.0.html https://reactjs.org/blog/2017/04/07/react-v15.5.0.html https://reactjs.org/blog/2017/06/13/react-v15.6.0.html

react-rails makes it easy to use React and JSX in your Ruby on Rails (3.2+) application. Learn more:


Install from Rubygems as react-rails.

gem "react-rails"

Get started with rails g react:install:

$ rails g react:install

Use with Webpacker

webpacker integrates modern JS tooling with Rails. ReactRailsUJS allows you to gradually migrate to webpacker.

Get started by adding webpacker to your gemfile and installing webpacker and react-rails:

$ rails webpacker:install
$ rails webpacker:install:react
$ rails generate react:install

This gives you:

When you add a component to components/, you can render it in a Rails view:

<%= react_component("HelloWorld", { greeting: "Hello" }) %>

The component name tells react-rails where to load the component. For example:

react_component call component require
react_component("Item") require("Item")
react_component("items/index") require("items/index")
react_component("items.Index") require("items").Index
react_component("items.Index.Header") require("items").Index.Header

This way, you can access top-level, default, or named exports.

If require fails, react-rails falls back to the global namespace approach described in Use with Asset Pipeline.

The require.context inserted into packs/application.js is used to load components. If you want to load components from a different directory, override it by calling ReactRailsUJS.useContext:

var myCustomContext = require.context("custom_components", true)
var ReactRailsUJS = require("react_ujs")
// use `custom_components/` for <%= react_component(...) %> calls

Use with Asset Pipeline

react-rails provides React.js & a UJS driver to the Rails asset pipeline. Get started by installing:

$ rails g react:install

Then restart your development server.

This will:

  • add some //= requires to application.js
  • add a components/ directory for React components
  • add server_rendering.js for server-side rendering

Now, you can create React components in .jsx files:

// app/assets/javascripts/components/post.jsx
window.Post = createReactClass({
  render: function() {
    return <h1>{this.props.title}</h1>
// or, equivalent:
class Post extends React.Component {
  render() {
    return <h1>{this.props.title}</h1>

Then, you can render those components in views:

<%= react_component("Post", {title: "Hello World"}) %>

Components must be accessible from the top level, but they may be namespaced, for example:

<%= react_component("Comments.NewForm", {post_id: @post.id}) %>
<!-- looks for `window.Comments.NewForm` -->

Custom JSX Transformer

react-rails uses a transformer class to transform JSX in the asset pipeline. The transformer is initialized once, at boot. You can provide a custom transformer to config.react.jsx_transformer_class. The transformer must implement:

  • #initialize(options), where options is the value passed to config.react.jsx_transform_options
  • #transform(code_string) to return a string of transformed code

react-rails provides two transformers, React::JSX::BabelTransformer (which uses ruby-babel-transpiler) and React::JSX::JSXTransformer (which uses the deprecated JSXTransformer.js).

React.js versions

//= require react brings React into your project.

By default, React's [development version] is provided to Rails.env.development. You can override the React build with a config:

# Here are the defaults: 
# config/environments/development.rb 
MyApp::Application.configure do
  config.react.variant = :development
# config/environments/production.rb 
MyApp::Application.configure do
  config.react.variant = :production

Be sure to restart your Rails server after changing these files. See VERSIONS.md to learn which version of React.js is included with your react-rails version.

View Helper

react-rails includes a view helper and an unobtrusive JavaScript driver which work together to put React components on the page.

The view helper (react_component) puts a div on the page with the requested component class & props. For example:

<%= react_component('HelloMessage', name: 'John') %>
<!-- becomes: -->
<div data-react-class="HelloMessage" data-react-props="{&quot;name&quot;:&quot;John&quot;}"></div>

On page load, the react_ujs driver will scan the page and mount components using data-react-class and data-react-props.

The view helper's signature is:

react_component(component_class_name, props={}, html_options={})
  • component_class_name is a string which identifies a component. See getConstructor for details.
  • props is either:
    • an object that responds to #to_json; or
    • an already-stringified JSON object (see JBuilder note below).
  • html_options may include:
    • tag: to use an element other than a div to embed data-react-class and data-react-props.
    • prerender: true to render the component on the server.
    • camelize_props to transform a props hash
    • **other Any other arguments (eg class:, id:) are passed through to content_tag.

Custom View Helper

react-rails uses a "helper implementation" class to generate the output of the react_component helper. The helper is initialized once per request and used for each react_component call during that request. You can provide a custom helper class to config.react.view_helper_implementation. The class must implement:

  • #react_component(name, props = {}, options = {}, &block) to return a string to inject into the Rails view
  • #setup(controller_instance), called when the helper is initialized at the start of the request
  • #teardown(controller_instance), called at the end of the request

react-rails provides one implementation, React::Rails::ComponentMount.


react-rails's JavaScript is available as "react_ujs" in the asset pipeline or from NPM. It attaches itself to the window as ReactRailsUJS.

Mounting & Unmounting

Usually, react-rails mounts & unmounts components automatically as described in Event Handling below.

You can also mount & unmount components from <%= react_component(...) %> tags using UJS:

// Mount all components on the page:
// Mount components within a selector:
// Mount components within a specific node:
// Unmounting works the same way:

You can use this when the DOM is modified by AJAX calls or modal windows.

Event Handling

ReactRailsUJS checks for various libraries to support their page change events:

  • Turbolinks
  • pjax
  • jQuery
  • Native DOM events

ReactRailsUJS will automatically mount components on <%= react_component(...) %> tags and unmount them when appropriate.

If you need to re-detect events, you can call detectEvents:

// Remove previous event handlers and add new ones:

For example, if Turbolinks is loaded after ReactRailsUJS, you'll need to call this again. This function removes previous handlers before adding new ones, so it's safe to call as often as needed.


Components are loaded with ReactRailsUJS.getConstructor(className). This function has two built-in implementations:

  • On the asset pipeline, it looks up className in the global namespace.
  • On webpacker, it requires files and accesses named exports, as described in Use with Webpacker.

You can override this function to customize the mapping of name-to-constructor. Server-side rendering also uses this function.

Server-Side Rendering

You can render React components inside your Rails server with prerender: true:

<%= react_component('HelloMessage', {name: 'John'}, {prerender: true}) %>
<!-- becomes: -->
<div data-react-class="HelloMessage" data-react-props="{&quot;name&quot;:&quot;John&quot;}">
  <h1>Hello, John!</h1>

(It will also be mounted by the UJS on page load.)

Server rendering is powered by ExecJS and subject to some requirements:

  • react-rails must load your code. By convention, it uses server_rendering.js, which was created by the install task. This file must include your components and their dependencies (eg, Underscore.js).
  • Your code can't reference document or window. Prerender processes don't have access to document or window, so jQuery and some other libs won't work in this environment :(

ExecJS supports many backends. CRuby users will get the best performance from mini_racer.


Server renderers are stored in a pool and reused between requests. Threaded Rubies (eg jRuby) may see a benefit to increasing the pool size beyond the default 0.

These are the default configurations:

# config/environments/application.rb 
# These are the defaults if you don't specify any yourself 
MyApp::Application.configure do
  # Settings for the pool of renderers: 
  config.react.server_renderer_pool_size  ||= 1  # ExecJS doesn't allow more than one on MRI 
  config.react.server_renderer_timeout    ||= 20 # seconds 
  config.react.server_renderer = React::ServerRendering::BundleRenderer
  config.react.server_renderer_options = { 
    files: ["server_rendering.js"],       # files to load for prerendering 
    replay_console: true,                 # if true, console.* will be replayed client-side 
  # Changing files matching these dirs/exts will cause the server renderer to reload: 
  config.react.server_renderer_extensions = ["jsx", "js"]
  config.react.server_renderer_directories = ["/app/assets/javascripts", "/app/javascripts/"]

JavaScript State

Some of ExecJS's backends are stateful (eg, mini_racer, therubyracer). This means that any side-effects of a prerender will affect later renders with that renderer.

To manage state, you have a couple options:

  • Make a custom renderer with #before_render / #after_render hooks as described below
  • Use per_request_react_rails_prerenderer to manage state for a whole controller action.

To check out a renderer for the duration of a controller action, call the per_request_react_rails_prerenderer helper in the controller class:

class PagesController < ApplicationController
  # Use the same React server renderer for the entire request: 

Then, you can access the ExecJS context directly with react_rails_prerenderer.context:

def show
  react_rails_prerenderer           # => #<React::ServerRendering::BundleRenderer> 
  react_rails_prerenderer.context   # => #<ExecJS::Context> 
  # Execute arbitrary JavaScript code 
  # `self` is the global context 
  render :show

react_rails_prerenderer may also be accessed in before- or after-actions.

Custom Server Renderer

react-rails depends on a renderer class for rendering components on the server. You can provide a custom renderer class to config.react.server_renderer. The class must implement:

  • #initialize(options={}), which accepts the hash from config.react.server_renderer_options
  • #render(component_name, props, prerender_options) to return a string of HTML

react-rails provides two renderer classes: React::ServerRendering::ExecJSRenderer and React::ServerRendering::BundleRenderer.

ExecJSRenderer offers two other points for extension:

  • #before_render(component_name, props, prerender_options) to return a string of JavaScript to execute before calling React.render
  • #after_render(component_name, props, prerender_options) to return a string of JavaScript to execute after calling React.render

Any subclass of ExecJSRenderer may use those hooks (for example, BundleRenderer uses them to handle console.* on the server).

Controller Actions

Components can also be server-rendered directly from a controller action with the custom component renderer. For example:

class TodoController < ApplicationController
  def index
    @todos = Todo.all
    render component: 'TodoList', props: { todos: @todos }, tag: 'span', class: 'todo'

You can also provide the "usual" render arguments: content_type, layout, location and status. By default, your current layout will be used and the component, rather than a view, will be rendered in place of yield. Custom data-* attributes can be passed like data: {remote: true}.

Prerendering is set to true by default, but can be turned off with prerender: false.

Component Generator

You can generate a new component file with:

rails g react:component ComponentName prop1:type prop2:type ...

For example,

rails g react:component Post title:string published:bool published_by:instanceOf{Person}

would generate:

var Post = createReactClass({
  propTypes: {
    title: PropTypes.string,
    published: PropTypes.bool,
    publishedBy: PropTypes.instanceOf(Person)
  render: function() {
    return (
        <div>Title: {this.props.title}</div>
        <div>Published: {this.props.published}</div>
        <div>Published By: {this.props.publishedBy}</div>

The generator also accepts options:

  • --es6: use class ComponentName extends React.Component
  • --coffee: use CoffeeScript

Accepted PropTypes are:

  • Plain types: any, array, bool, element, func, number, object, node, shape, string
  • instanceOf takes an optional class name in the form of instanceOf{className}.
  • oneOf behaves like an enum, and takes an optional list of strings in the form of 'name:oneOf{one,two,three}'.
  • oneOfType takes an optional list of react and custom types in the form of 'model:oneOfType{string,number,OtherType}'.

Note that the arguments for oneOf and oneOfType must be enclosed in single quotes to prevent your terminal from expanding them into an argument list.

Use with JBuilder

If you use Jbuilder to pass a JSON string to react_component, make sure your JSON is a stringified hash, not an array. This is not the Rails default -- you should add the root node yourself. For example:

# BAD: returns a stringified array 
json.array!(@messages) do |message|
  json.extract! message, :id, :name
  json.url message_url(message, format: :json)
# GOOD: returns a stringified hash 
json.messages(@messages) do |message|
  json.extract! message, :id, :name
  json.url message_url(message, format: :json)

Camelize Props

You can configure camelize_props option:

MyApp::Application.configure do
  config.react.camelize_props = true # default false 

Now, Ruby hashes given to react_component(...) as props will have their keys transformed from underscore- to camel-case, for example:

{ all_todos: @todos, current_status: @status }
# becomes: 
{ "allTodos" => @todos, "currentStatus" => @status }

You can also specify this option in react_component:

<%= react_component('HelloMessage', {name: 'John'}, {camelize_props: true}) %>

Related Projects


  • Run tests with rake test or appraisal rake test
    • Integration tests run in Headless Chrome which is included in Chrome (59+ linux,OSX | 60+ Windows)
    • ChromeDriver is included with chromedriver-helper gem so no need to manually install that 👍
  • Update React assets with rake react:update
  • Update the UJS with rake ujs:update
  • Releases:
    • To release a new RubyGems version:
      • Increment the version in lib/react/rails/version.rb
      • Add an entry to VERSIONS.md
      • Update the changelog (find recent changes on GitHub by listing commits or showing closed PRs)
      • Commit changes & push to master
      • bundle exec rake release: pushes a tag to GitHub, builds a .gem, and pushes to RubyGems
    • To release a new NPM version:
      • Update the version in react_ujs/package.json
      • Commit & push to master
      • bundle exec rake ujs:publish (runs npm publish)




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