ASP.NET Core,  React,  SPA

React code splitting and server-side rendering with ASP.NET Core – Part 1

Thanks to webpack, code splitting has become easy with dynamic import. However, for code splitting to work together with server-side rendering, things become more tricky and not that straight forward because at the server side, the modules have to be loaded synchronously in order to render the page correctly. There are several different available loaders that can help get the job done, with the correct configuration and implementation. Or using the simpler and easier method I would like to share in the Part 2 of this post.

This post will be break down into 2 parts:

Part 1: Enabling code splitting

Part 2: Support code splitting with server side rendering

Enable react code splitting

Goal: To enable code splitting (with redux-first-router)

Prerequisite: Some experience with ReactRedux and redux-first-router. Check out my Get started series if needed.

Base project code: Example code from From redux-little-router to redux-first-router for React/Redux SPA will be used as starting point.

Dynamic Import

syntax: var promise: Promise<any> = import('./AnyReactComponent')

Calling import within code will dynamically load the module and returns a promise. Once the module finishes loading, the promise resolves and return the module for use. When bundling using webpack, webpack will code split this module as a separate file and only load the module when import is invoked.

Important: path to the component file should use literal string. (variable shall not be used or webpack will not be able to do the code splitting correctly)

Asynchronous React Component

To enable dynamic loading of the module, we use a React component (loader) as a wrapper. This wrapper component will only import the actual module when the corresponding page is shown. Let’s create the a new file AsyncComponent.tsx under Scripts folder with following codes:

This is a basic version (no error handling) of an asynchronous component to load the module on demand. A loader (function) is passed as a property to AsyncComponent. When the component is mounted, it will invoke the loader and start downloading the actual module for display. Once the module is loaded, the default export will be used  as React component for rendering. Below shows an example of the loader:

() => import('./Contact')

Note: there are several react packages that offer more sophisticated asynchronous loader including react-loadable, react-async-component, react-universal-component and etc. For the purpose of this tutorial, we will simply use the basic one.

Modules for code splitting

Next we create separate files for About page and Contact page:



Finally, we will update  routes.tsx to use AsyncComponent for code splitting.

Add following codes:

Then replace the Components variable in routes.tsx as follow:

Use of key property is for React to identify that those are different AsyncComponent instances.

Typescript configuration

Webpack code-splitting would not work with default module target (CommonJS). The module target should be set to esnext. So let’s add the following lines to tsconfig.json

That’s it. Build and run and you have About and Contact pages loaded on demand!

Important: So far we have taken care of code splitting at client side. But it’s not working correctly at server side rendering yet. Guess what the problem is. We will discuss and resolve the problem in part 2. Stay tuned!

Example code is available at Github.

Next > Support code splitting with server side rendering


  • Pascal

    Thanks ! A simple project that compiles…

    I tried several projects but I didn’t find a good Aspnet Core + Typescipt + Redux solution for code splitting.

    When do you plan to publish part 2 SSR (or at least the source code) ?

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