React Server Rendering

See also Client vs. Server Rendering.

What is the easiest way to set up a Webpack configuration for server-side-rendering?

See the example Webpack setup here: github.com/shakacode/react_on_rails_demo_ssr_hmr.

What is Server Rendering?

Here's a decent article to introduce you to server rendering. Note, React on Rails takes care of calling the methods in ReactDOMServer.

During the Rails rendering of HTML per a browser request, the Rails server will execute some JavaScript to create a string of HTML used for React server rendering. This resulting HTML is placed with in your Rails view's output.

The default JavaScript interpreter is ExecJS. If you want to maximize the performance of your server rendering, then you want to use React on Rails Pro which uses NodeJS to do the server rendering. See the docs for React on Rails Pro.

See this note.

How do you do Server Rendering with React on Rails?

1. The react_component view helper method provides the prerender: option to switch on or off server rendering.
2. Configure your Webpack setup to create a different server bundle per your needs. While you may reuse the same bundle as for client rendering, this is not common in larger apps for many reasons, such as code splitting, handling CSS and images, different code paths for React Router on the server vs. client, etc.
3. You need to configure config.server_bundle_js_file = "server-bundle.js" in your config/initializers/react_on_rails.rb
4. You should not put a hash on the server-bundle so that you can easily use the webpack-dev-server for client bundles and have the server bundle generated by a watch process.

Do you need server rendering?

Server rendering is used for either SEO or performance reasons.

Considerations for what code can run on in server rendering

1. Never access window. Animations, globals on window, etc. just don't make sense when you're trying to run some JavaScript code to output a string of HTML.
2. JavaScript calls to setTimeout, setInterval, and clearInterval similarly don't make sense when server rendering.
3. Promises and file system access don't work when server rendering with ExecJS. Instead, you can use the Node renderer or React on Rails Pro.

For a comprehensive list of ExecJS constraints, see ExecJS Limitations.

:::tip Pro Upgrade React on Rails Pro includes a dedicated Node.js renderer that eliminates ExecJS limitations and improves SSR performance by 3-10x. It also supports streaming SSR with React 18/19's renderToPipeableStream for faster Time to First Byte. Learn more → :::