Dynamic micro frontends with Nx and React

When there are a lot of teams on the project, when dynamic frontend expansion is necessary, and when a rebuild of the entire project is not an option, the concept of Micro Frontends comes into play in conjunction with Dynamic Module Federation.

Nx has a great tutorial for angular stack on this topic. Let's try to implement this concept for react stack.

The Nx documentation says:

Nx is a smart, fast and extensible build system with first class monorepo support and powerful integrations.

Now we will check it in practice, we will generate several applications and a helper library.

Create Nx workspace

To create Nx workspace, run the command:

npx create-nx-workspace@latest

Choose a name and type (apps), Nx Cloud can be left unconnected.

Generation of host-app and children apps

Install @nrwl/react plugin as dev dependency. It provides handy generators and utilities that make it easy to manage React apps and libraries inside the Nx workspace.

npm install -D @nrwl/react

Create host-app and micro frontends:

npx nx g @nrwl/react:host host --remotes=cart,blog,shop

Select the styling settings you need in applications and wait for the end of the generation.

Creating a library for easy registration and import of micro frontends

To import micro frontends dynamically by URL, we need to create a library that will help with this. To do this, we will generate a library using the @nrwl/js generator and call it load-remote-module.

npx nx g @nrwl/js:library load-remote-module

Let's add the code to the freshly generated library /libs/load-remote-module/src/lib/load-remote-module.ts:

export type ResolveRemoteUrlFunction = (
  remoteName: string
) => string | Promise<string>;

declare const __webpack_init_sharing__: (scope: 'default') => Promise<void>;
declare const __webpack_share_scopes__: { default: unknown };

let resolveRemoteUrl: ResolveRemoteUrlFunction;

export function setRemoteUrlResolver(
  _resolveRemoteUrl: ResolveRemoteUrlFunction
) {
  resolveRemoteUrl = _resolveRemoteUrl;
}

let remoteUrlDefinitions: Record<string, string>;

export function setRemoteDefinitions(definitions: Record<string, string>) {
  remoteUrlDefinitions = definitions;
}

let remoteModuleMap = new Map<string, unknown>();
let remoteContainerMap = new Map<string, unknown>();

export async function loadRemoteModule(remoteName: string, moduleName: string) {
  const remoteModuleKey = `${remoteName}:${moduleName}`;
  if (remoteModuleMap.has(remoteModuleKey)) {
    return remoteModuleMap.get(remoteModuleKey);
  }

  const container = remoteContainerMap.has(remoteName)
    ? remoteContainerMap.get(remoteName)
    : await loadRemoteContainer(remoteName);

  const factory = await container.get(moduleName);
  const Module = factory();

  remoteModuleMap.set(remoteModuleKey, Module);

  return Module;
}

function loadModule(url: string) {
  return import(/* webpackIgnore:true */ url);
}

let initialSharingScopeCreated = false;

async function loadRemoteContainer(remoteName: string) {
  if (!resolveRemoteUrl && !remoteUrlDefinitions) {
    throw new Error(
      'Call setRemoteDefinitions or setRemoteUrlResolver to allow Dynamic Federation to find the remote apps correctly.'
    );
  }

  if (!initialSharingScopeCreated) {
    initialSharingScopeCreated = true;
    await __webpack_init_sharing__('default');
  }

  const remoteUrl = remoteUrlDefinitions
    ? remoteUrlDefinitions[remoteName]
    : await resolveRemoteUrl(remoteName);

  const containerUrl = `${remoteUrl}${
    remoteUrl.endsWith('/') ? '' : '/'
  }remoteEntry.js`;

  const container = await loadModule(containerUrl);
  await container.init(__webpack_share_scopes__.default);

  remoteContainerMap.set(remoteName, container);
  return container;
}

This code is based on code from the Nx plugin for angular.

Register the load-remote-module library in our host-application /apps/host/webpack.config.js:

const withModuleFederation = require('@nrwl/react/module-federation');
const moduleFederationConfig = require('./module-federation.config');

const coreLibraries = new Set([
  'react',
  'react-dom',
  'react-router-dom',
  '@microfrontends/load-remote-module',
]);

module.exports = withModuleFederation({
  ...moduleFederationConfig,
  shared: (libraryName, defaultConfig) => {
    if (coreLibraries.has(libraryName)) {
      return {
        ...defaultConfig,
        eager: true,
      };
    }

    // Returning false means the library is not shared.
    return false;
  },
});

Registration is required to avoid the error: Uncaught Error: Shared module is not available for eager consumption.

Configuration and Connecting micro frontends

Let's save a list of links to our micro frontends in JSON file format - this is one of the easiest methods to get them at runtime, on the host-app side, all that remains is to make a GET request. In the future, we may use the server API for this purpose.

Create a file module-federation.manifest.json in folder /apps/host/src/assets/module-federation.manifest.json:

{
  "cart": "http://localhost:4201",
  "blog": "http://localhost:4202",
  "shop": "http://localhost:4203"
}

Open /apps/host/src/main.ts and change for:

import { setRemoteDefinitions } from '@microfrontends/load-remote-module';
import('./bootstrap');

fetch('/assets/module-federation.manifest.json')
  .then((res) => res.json())
  .then((definitions) => setRemoteDefinitions(definitions))
  .then(() => import('./bootstrap').catch((err) => console.error(err)));

As you can see, we:

• Fetch JSON file
• Call setRemoteDefinitions with its contents
• This allows webpack to understand where our micro frontends are deployed

Change the method of loading micro frontends in the host-app to dynamic

At the moment, webpack determines where the micro frontends are located during the build step, as it is specified in the /apps/host/module-federation.config.js config file.

Open module-federation.config.js, which is located in our host-app folder /apps/host/module-federation.config.js, and set the value of remotes to an empty array so that webpack does not look for modules when building. It will look like this:

module.exports = {
  name: 'host',
  remotes: [],
};

Next, we need to change the way micro frontends are loaded in our host-app. Open the file /apps/host/src/app/app.tsx and replace the import code with:

import { loadRemoteModule } from '@microfrontends/load-remote-module';

const Cart = React.lazy(() => loadRemoteModule('cart', './Module'));

const Blog = React.lazy(() => loadRemoteModule('blog', './Module'));

const Shop = React.lazy(() => loadRemoteModule('shop', './Module'));

That's all it takes to replace Static Module Federation to Dynamic Module Federation.

Serve and check

To serve our host-app and micro frontends:

npm run start

Or the parallel start of all apps:

nx run-many --parallel --target=serve --projects=host,cart,blog,shop --maxParallel=100

Open localhost:4200 and see, what our micro frontends Dynamic Module Federation is working:

• config is fetching from module-federation.manifest.json via GET request
• if you remove one of the applications from it, then we will get an error in the browser
• we can add additional micro frontends

---

GitHub repository - dynamic-micro-frontends-with-Nx-and-react.

Additional info:

• dynamic-module-federation-with-angular
• Monorepos in JavaScript & TypeScript
• Nx docs

Big thanks to ScorIL for the help with the load-remote-module library.