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Getting Started

Note, the best way to understand how to use ReactOnRails is to study a few simple examples. You can do a quick demo setup, either on your existing app or on a new Rails app.

  1. Do the quick tutorial.
  2. Add React on Rails to an existing Rails app per the instructions.
  3. Look at spec/dummy, a simple, no DB example.
  4. Look at; it's a full-featured example live at

Basic Installation

See also the instructions for installing into an existing Rails app.

  1. Add the react_on_rails gem to Gemfile:

    bundle add react_on_rails --strict
  2. Commit this to git (or else you cannot run the generator unless you pass the option --ignore-warnings).

  3. Run the generator:

    rails generate react_on_rails:install
  4. Start the app:

    rails s
  5. Visit http://localhost:3000/hello_world.

Turning on server rendering

With the code from running the React on Rails generator above:

  1. Edit app/views/hello_world/index.html.erb and set the prerender option to true.
  2. Refresh the page.

Below is the line where you turn server rendering on by setting prerender to true:

<%= react_component("HelloWorld", props: @hello_world_props, prerender: false) %>

Note, if you got an error in your console regarding "ReferenceError: window is not defined", then you need to edit config/webpacker.yml and set hmr: false and inline: false. See rails/webpacker PR 2644 for a fix for this issue.

Basic Usage


  • Configure config/initializers/react_on_rails.rb. You can adjust some necessary settings and defaults. See file docs/basics/ for documentation of all configuration options.
  • Configure config/webpacker.yml. If you used the generator and the default webpacker setup, you don't need to touch this file. If you are customizing your setup, then consult the spec/dummy/config/webpacker.yml example or the official default webpacker.yml.
  • Most apps should rely on the rails/webpacker setup for Webpack. v6 of rails/webpacker includes support for v5 of webpack.

Including your React Component on your Rails Views

  • React component are rendered via your Rails Views. Here's an ERB sample:

    <%= react_component("HelloWorld", props: @some_props) %>
  • Server-Side Rendering: Your react component is first rendered into HTML on the server. Use the prerender option:

    <%= react_component("HelloWorld", props: @some_props, prerender: true) %>
  • The component_name parameter is a string matching the name you used to expose your React component globally. So, in the above examples, if you had a React component named "HelloWorld", you would register it with the following lines:

    import ReactOnRails from 'react-on-rails';
    import HelloWorld from './HelloWorld';
    ReactOnRails.register({ HelloWorld });

    Exposing your component in this way is how React on Rails is able to reference your component from a Rails view. You can expose as many components as you like, as long as their names do not collide. See below for the details of how you expose your components via the react_on_rails webpack configuration. You may call ReactOnRails.register many times.

  • @some_props can be either a hash or JSON string. This is an optional argument assuming you do not need to pass any options (if you want to pass options, such as prerender: true, but you do not want to pass any properties, simply pass an empty hash {}). This will make the data available in your component:

      # Rails View
      <%= react_component("HelloWorld", props: { name: "Stranger" }) %>
  • This is what your HelloWorld.js file might contain. The railsContext is always available for any parameters that you always want available for your React components. It has nothing to do with the concept of the React Context. See Render-Functions and the RailsContext for more details on this topic.

    import React from 'react';
    export default (props, railsContext) => {
      // Note wrap in a function to make this a React function component
      return () => (
          Your locale is {railsContext.i18nLocale}.<br/>
          Hello, {}!

See the View Helpers API for more details on react_component and its sibling function react_component_hash.

Globally Exposing Your React Components

For the React on Rails view helper react_component to use your React components, you will have to register them in your JavaScript code.

Use modules just as you would when using Webpack and React without Rails. The difference is that instead of mounting React components directly to an element using React.render, you register your components to ReactOnRails and then mount them with helpers inside of your Rails views.

This is how to expose a component to the react_component view helper.

  // app/javascript/packs/hello-world-bundle.js
  import HelloWorld from '../components/HelloWorld';
  import ReactOnRails from 'react-on-rails';
  ReactOnRails.register({ HelloWorld });

Different Server-Side Rendering Code (and a Server-Specific Bundle)

You may want different code for your server-rendered components running server side versus client side. For example, if you have an animation that runs when a component is displayed, you might need to turn that off when server rendering. One way to handle this is conditional code like if (window) { doClientOnlyCode() }.

Another way is to use a separate webpack configuration file that can use a different server side entry file, like 'serverRegistration.js' as opposed to 'clientRegistration.js.' That would set up different code for server rendering.

For details on techniques to use different code for client and server rendering, see: How to use different versions of a file for client and server rendering. (Requires creating a free account.)

Specifying Your React Components: Register directly or use render-functions

You have two ways to specify your React components. You can either register the React component (either function or class component) directly, or you can create a function that returns a React component, which we using the name of a "render-function". Creating a render-function allows:

  1. You to have access to the railsContext. See documentation for the railsContext in terms of why you might need it. You need a Render-Function to access the railsContext.
  2. You can use the passed-in props to initialize a redux store or set up react-router.
  3. You can return different components depending on what's in the props.

Note, the return value of a Render-Function should be either a React Function or Class Component, or an object representing server rendering results.

Do not return a React Element (JSX).

ReactOnRails will automatically detect a registered Render-Function by the fact that the function takes more than 1 parameter. In other words, if you want the ability to provide a function that returns the React component, then you need to specify at least a second parameter. This is the railsContext. If you're not using this parameter, declare your function with the unused param:

const MyComponentGenerator = (props, _railsContext) => {
  if (props.print) {
    // This is a React FunctionComponent because it is wrapped in a function.
    return () => <H1>{JSON.stringify(props)}</H1>;

Thus, there is no difference between registering a React Function Component or class Component versus a "Render-Function." Just call ReactOnRails.register.

react_component_hash for Render-Functions

Another reason to use a Render-Function is that sometimes in server rendering, specifically with React Router, you need to return the result of calling ReactDOMServer.renderToString(element). You can do this by returning an object with the following shape: { renderedHtml, redirectLocation, error }. Make sure you use this function with react_component_hash.

For server rendering, if you wish to return multiple HTML strings from a Render-Function, you may return an Object from your Render-Function with a single top-level property of renderedHtml. Inside this Object, place a key called componentHtml, along with any other needed keys. An example scenario of this is when you are using side effects libraries like React Helmet. Your Ruby code will get this Object as a Hash containing keys componentHtml and any other custom keys that you added:

{ renderedHtml: { componentHtml, customKey1, customKey2} }

For details on using react_component_hash with react-helmet, see our react-helmet documentation.

Error Handling

  • All errors from ReactOnRails will be of type ReactOnRails::Error.
  • Prerendering (server rendering) errors get context information for HoneyBadger and Sentry for easier debugging.


React on Rails provides an option for automatic conversions of Rails *.yml locale files into *.json or `.js. See the How to add I18n for a summary of adding I18n.