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Upgrading React on Rails

Need Help Migrating?

If you would like help in migrating between React on Rails versions or help with implementing server rendering, please contact [email protected] for more information about our React on Rails Pro Support.

We specialize in helping companies to quickly and efficiently upgrade. The older versions use the Rails asset pipeline to package client assets. The current and recommended way is to use Webpack 4+ for asset preparation. You may also need help migrating from the rails/webpacker's Webpack configuration to a better setup ready for Server Side Rendering.

Upgrading to v13

Breaking Change

Previously, the gem webpacker was a Gem dependency.

v13 has changed slightly to switch to shakapacker.

For details, see the Shakapacker guide to upgrading to version 6 and version 7

In summary:

  1. Change the gem reference from 'webpacker' to 'shakapacker'
  2. Change the npm reference from '@rails/webpacker' to 'shakapacker'
  3. Other updates, depending on what version of rails/webpacker that you had.

Upgrading to v12

Recent versions

Make sure that you are on a relatively more recent version of rails and webpacker. Yes, the rails/webpacker gem is required! v12 is tested on Rails 6. It should work on Rails v5. If you're on any older version, and v12 doesn't work, please file an issue.

Remove config.symlink_non_digested_assets_regex from your config/initializers/react_on_rails.rb. If you still need that feature, please file an issue.

i18n default format changed to JSON

  • If you're using the internalization helper, then set config.i18n_output_format = 'js'. You can later update to the default JSON format as you will need to update your usage of that file. A JSON format is more efficient.

Updated API for ReactOnRails.register()

In order to solve the issues regarding React Hooks compatibility, the number of parameters for functions is used to determine if you have a Render-Function that will get invoked to return a React component, or you are registering a React component defined by a function. Please see Render-Functions and the Rails Context for more information on what a Render-Function is.

Update required for registered functions taking exactly 2 params.

Registered Objects are of the following type:

  1. Function that takes only zero or one params and you return a React Element, often JSX. If the function takes zero or one params, there is no migration needed for that function.

    export default (props) => <Component {...props} />;
  2. Function that takes only zero or one params and you return an Object (not a React Element). If the function takes zero or one params, you need to add one or two unused params so you have exactly 2 params and then that function will be treated as a render function and it can return an Object rather than a React element. If you don't do this, you'll see this obscure error message:

  [SERVER] message: Objects are not valid as a React child (found: object with keys {renderedHtml}). If you meant to render a collection of children, use an array instead.
  in YourComponentRenderFunction

So look in YourComponentRenderFunction and do this change

   export default (props) => { renderedHTML: getRenderedHTML };

To have exactly 2 arguments:

    export default (props, _railsContext) => { renderedHTML: getRenderedHTML };
  1. Function that takes 2 params and returns a React function or class component. Migration is needed as the older syntax returned a React Element. A function component is a function that takes zero or one params and returns a React Element, like JSX. The correct syntax looks like:
    export default (props, railsContext) => () => <Component {{...props, railsContext}} />;
    Note, you cannot return a React Element (JSX). See below for the migration steps. If your function that took two params returned an Object, then no migration is required.
  2. Function that takes 3 params and uses the 3rd param, domNodeId, to call ReactDOM.hydrate. If the function takes 3 params, there is no migration needed for that function.
  3. ES6 or ES5 class. There is no migration needed.

Previously, with case number 2, you could return a React Element.

The fix is simple. Here is an example of the change you'll do:

2020-07-07_09-43-51 (1)
Broken, as this function takes two params and it returns a React Element from a JSX Literal
export default (props, railsContext) => <Component {{...props, railsContext} />;

If you make this mistake, you'll get this warning Warning: React.createElement: type is invalid -- expected a string (for built-in components) or a class/function (for composite components) but got: <Fragment />. Did you accidentally export a JSX literal instead of a component?

And this error: react-dom.development.js:23965 Uncaught Error: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object.

In this example, you need to wrap the <Component {...props} /> in a function call like this which results in the return value being a React function component.

export default (props, _railsContext) => () => <Component {...props} />;

If you have a pure component, taking one or zero parameters, and you have an unnecessary function wrapper such that you're returning a function rather than a React Element, then:

  1. You won't see anything render.
  2. You will see this warning in development mode: Warning: Functions are not valid as a React child. This may happen if you return a Component instead of <Component /> from render. Or maybe you meant to call this function rather than return it.

Upgrading rails/webpacker from v3 to v4

Custom Webpack build file

The default value for extract_css is false in config/webpack.yml. Custom webpack builds should set this value to true or else no CSS link tags are generated. You have a custom webpack build if you are not using rails/webpacker to setup your Webpack configuration.

default: &default
   # other stuff
   extract_css: true
   # by default, extract and emit a css file. The default is false

Upgrading to version 11

  • Remove server_render_method from config/initializers/react_on_rails.rb. Alternate server rendering methods are part of React on Rails Pro. If you want to use a custom renderer, contact [email protected]. We have a custom node rendering solution in production for
  • Remove your usage of ENV["TRACE_REACT_ON_RAILS"] usage. You can get all tracing with either specifying trace at your component or in your config/initializers/react_on_rails.rb file.
  • ReactOnRails::Utils.server_bundle_file_name and ReactOnRails::Utils.bundle_file_name were removed. React on Rails Pro contains upgrades to enable component and other types caching with React on Rails.

Upgrading to version 10

Pretty simple:

  • Follow the steps to migrate to version 9 (except installing 10.x instead of 9.x)
  • If you have react_component returning hashes, then switch to react_component_hash instead

Upgrading to version 9

Why Webpacker?

Webpacker provides areas of value:

  • View helpers that support bypassing the asset pipeline, which allows you to avoid double minification and enable source maps in production. This is 100% a best practice as source maps in production greatly increases the value of services such as HoneyBadger or Sentry.
  • A default Webpack config so that you only need to do minimal modifications and customizations. However, if you're doing server rendering, you may not want to give up control. Since Webpacker's default webpack config is changing often, we at Shakacode can give you definitive advice on webpack configuration best practices. In general, if you're happy with doing your own Webpack configuration, then we suggest using the client strategy discussed below. Most corporate projects will prefer having more control than direct dependence on webpacker easily allows.

Integrating Webpacker

Reason for doing this: This enables your webpack bundles to bypass the Rails asset pipeline and it's extra minification, enabling you to use source-maps in production, while still maintaining total control over everything in the client directory

From version 7 or lower

...while keeping your client directory
  • .gitignore: add /public/webpack/*
  • Gemfile: bump react_on_rails and add webpacker
  • layout views: anything bundled by webpack will need to be requested by a javascript_pack_tag or stylesheet_pack_tag.
  • Search your codebase for javascript_include_tag. Use the
  • config/initializers/assets.rb: we no longer need to modify Rails.application.config.assets.paths or append anything to Rails.application.config.assets.precompile.
  • config/initializers/react_on_rails.rb:
    • Delete config.generated_assets_dir. Webpacker's config now supplies this information
    • Replace config.npm_build_(test|production)_command with config.build_(test|production)_command
  • config/webpacker.yml: start with our example config (feel free to modify it as needed). I recommend setting dev_server.hmr to false however since HMR is currently broken.
  • client/package.json: bump react_on_rails (I recommend bumping webpack as well). You'll also need js-yaml if you're not already using eslint and webpack-manifest-plugin regardless.
Client Webpack config:
  • You'll need the following code to read data from the webpacker config:
const path = require('path');
const ManifestPlugin = require('webpack-manifest-plugin'); // we'll use this later

const webpackConfigLoader = require('react-on-rails/webpackConfigLoader');
const configPath = path.resolve('..', 'config');
const { output } = webpackConfigLoader(configPath);
  • That output variable will be used for webpack's output rules:
  output: {
    filename: '[name]-[chunkhash].js', // [chunkhash] because we've got to do our own cache-busting now
    path: output.path,
    publicPath: output.publicPath,
  • well as for the output of plugins like webpack-manifest-plugin:

      new ManifestPlugin({
        publicPath: output.publicPath,
        writeToFileEmit: true
  • If you're using referencing files or images with url-loader & file-loader, their publicpaths will have to change as well: publicPath: '/webpack/',
  • If you're using css-loader, webpack.optimize.CommonsChunkPlugin, or extract-text-webpack-plugin, they will also need cache-busting!

...and you're finally done!

...while replacing your client directory
  • Make the same changes to config/initializers/react_on_rails.rb as described above
  • Upgrade RoR & add Webpacker in the Gemfile
  • Upgrade RoR in the client/package.json
  • Run bundle
  • Run rails webpacker:install
  • Run rails webpacker:install:react
  • Run rails g react_on_rails:install
  • Move your entry point files to app/javascript/packs
  • Either:
    • Move all your source code to app/javascript/bundles, move your linter configs to the root directory, and then delete the client directory
    • or just delete the webpack config and remove webpack, its loaders, and plugins from your client/package.json.

...and you're done.

From version 8

For an example of upgrading, see react-webpack-rails-tutorial/pull/416.

  • Breaking Configuration Changes

    1. Added config.node_modules_location which defaults to "" if Webpacker is installed. You may want to set this to 'client'toconfig/initializers/react_on_rails.rbto keep your node_modules inside of/client`
    2. Renamed
    • config.npm_build_test_command ==> config.build_test_command
    • config.npm_build_production_command ==> config.build_production_command
  • Update the gemfile. Switch over to using the webpacker gem.

gem "webpacker"
  • Update for the renaming in the WebpackConfigLoader in your webpack configuration. You will need to rename the following object properties:

    • webpackOutputPath ==> output.path
    • webpackPublicOutputDir ==> output.publicPath
    • hotReloadingUrl ==> output.publicPathWithHost
    • hotReloadingHostname ==>
    • hotReloadingPort ==> settings.dev_server.port
    • hmr ==> settings.dev_server.hmr
    • manifest ==> Remove this one. We use the default for Webpack of manifest.json
    • env ==> Use const { env } = require('process');
    • devBuild ==> Use const devBuild = process.env.NODE_ENV !== 'production';
  • Edit your Webpack.config files:

    • Change your Webpack output to be like this. Be sure to have the hash or chunkhash in the filename, unless the bundle is server side.:
      const webpackConfigLoader = require('react-on-rails/webpackConfigLoader');
      const configPath = resolve('..', 'config');
      const { output, settings } = webpackConfigLoader(configPath);
      const hmr = settings.dev_server.hmr;
      const devBuild = process.env.NODE_ENV !== 'production';
      output: {
        filename: isHMR ? '[name]-[hash].js' : '[name]-[chunkhash].js',
        chunkFilename: '[name]-[chunkhash].chunk.js',
        publicPath: output.publicPath,
        path: output.path,
    • Change your ManifestPlugin definition to something like the following
      new ManifestPlugin({
          publicPath: output.publicPath,
          writeToFileEmit: true
  • Find your webpacker_lite.yml and rename it to webpacker.yml

    • Consider copying a default webpacker.yml setup such as
    • If you are not using the webpacker webpacker setup, be sure to put in compile: false in the default section.
    • Alternately, if you are updating from webpacker_lite, you can manually change these:
    • Add a default setting
      cache_manifest: false
    • For production, set:
      cache_manifest: true
    • Add a section like this under your development env:
        host: localhost
        port: 3035
        hmr: false
      Set hmr to your preference.
    • See the example spec/dummy/config/webpacker.yml.
    • Remove keys hot_reloading_host and hot_reloading_enabled_by_default. These are replaced by the dev_server key.
    • Rename webpack_public_output_dir to public_output_path.
  • Edit your

    • Remove the env value WEBPACKER_DEV_SERVER as it's not used
    • For hot loading:
      • Set the hmr key in your webpacker.yml to true.

Without integrating webpacker

  • Bump your ReactOnRails versions in Gemfile & package.json
  • In /config/initializers/react_on_rails.rb:
    • Rename config.npm_build_test_command ==> config.build_test_command
    • Rename config.npm_build_production_command ==> config.build_production_command
    • Add config.node_modules_location = "client"

...and you're done.