The Micro Frontend is one of the hottest topics on the internet right now. We hear it all the time, but what is micro Frontend? Imagine a website with lots of components such as Navbar, Footer, Main Container and Side Menu. What would happen, if they were being served from different domains? Yes, you guessed it right we would've ended up with a micro Frontend. Now, thanks to micro frontend technologies, we can deal with those apps separately. We can write their unit tests separately, e2e tests separately we can even use different frameworks like Angular, Vue and Svelte.
There are two major players to make those things happen right now, one of them is Module Federation and another one is Single SPA which I covered here: 🔗Migrating CRA to Micro Frontends with Single SPA.
Unlike Single SPA, Module Federation is lot less opiniated. You can architect your project however you want in Module Federation whereas in Single SPA you need setup a config file and architect your project around this file.
And there is only one thing scary about micro Frontends, and, that is configurations. Initial configuration scares people away because there are lots of pieces you need to bring together, and if it's your first time, without guidance, it's so easy to get lost.
Working Example
This a POC(Proof of Concept) project it may not look great, but that's not the point in our case.
Module Federation
The Module Federation is actually part of Webpack config. This config enables us to expose or receive different parts of the CRA to another CRA project.
These separate project should not have dependencies between each other, so they can be developed and deployed individually.
Let's first start by creating our Container project which exports other two app APP-1 and APP-2.
npx create-react-app container --template typescript Container App
Project Structure
container ├─ package.json ├─ public │ ├─ index.dev.html │ └─ index.prod.html ├─ src │ ├─ App.tsx │ ├─ bootstrap.tsx │ └─ index.ts ├─ tsconfig.json ├─ webpack.config.js ├─ webpack.prod.js └─ yarn.lock Let's add our dependencies
yarn add html-webpack-plugin serve ts-loader webpack webpack-cli webpack-dev-server We need to make some changes. Create a file called bootstrap.tsx and move index.ts into bootstrap.tsx.
bootstrap.tsx
import App from './App'; import React from 'react'; import ReactDOM from 'react-dom'; ReactDOM.render(<App />, document.getElementById('root')); And add those into index.ts
index.ts
import('./bootstrap'); export {}; And, finally add those into app.tsx for future use. We will discuss them later.
app.tsx
import React from 'react'; //@ts-ignore import CounterAppTwo from 'app2/CounterAppTwo'; //@ts-ignore import CounterAppOne from 'app1/CounterAppOne'; export default () => ( <div style={{ margin: '20px' }}> <React.Suspense fallback="Loading header..."> <div style={{ border: '1px dashed black', height: '50vh', display: 'flex', justifyContent: 'space-around', alignItems: 'center', flexDirection: 'column', }} > <h1>CONTAINER</h1> <div style={{ display: 'flex', flexDirection: 'row', justifyContent: 'space-around', }} > <div style={{ marginRight: '2rem', padding: '2rem', border: '1px dashed black', }} > <h2>APP-1</h2> <CounterAppOne /> </div> <div style={{ border: '1px dashed black', padding: '2rem' }}> <h2>APP-2</h2> <CounterAppTwo /> </div> </div> </div> </React.Suspense> </div> ); We've completed component parts and here comes the critical part. We need to setup our container apps Webpack to receive app-1 and app-2.
webpack.config.js
const HtmlWebpackPlugin = require('html-webpack-plugin'); const { ModuleFederationPlugin } = require('webpack').container; const path = require('path'); const deps = require('./package.json').dependencies; module.exports = { entry: './src/index.ts', mode: 'development', devServer: { contentBase: path.join(__dirname, 'dist'), port: 3000, }, output: { publicPath: 'http://localhost:3000/', }, resolve: { extensions: ['.ts', '.tsx', '.js'], }, module: { rules: [ { test: /.(js|jsx|tsx|ts)$/, loader: 'ts-loader', exclude: /node_modules/, }, ], }, plugins: [ new ModuleFederationPlugin({ name: 'container', library: { type: 'var', name: 'container' }, remotes: { app1: 'app1', app2: 'app2', }, shared: { ...deps, react: { singleton: true, eager: true, requiredVersion: deps.react }, 'react-dom': { singleton: true, eager: true, requiredVersion: deps['react-dom'], }, }, }), new HtmlWebpackPlugin({ template: './public/index.dev.html', }), ], }; Update your package.json scripts as follows:
"scripts": { "start": "webpack serve --open", "build": "webpack --config webpack.prod.js", "serve": "serve dist -p 3002", "clean": "rm -rf dist" } Update your tsconfig as follows:
{ "compilerOptions": { "target": "es5", "lib": ["dom", "dom.iterable", "esnext"], "allowJs": true, "skipLibCheck": true, "esModuleInterop": true, "allowSyntheticDefaultImports": true, "strict": true, "forceConsistentCasingInFileNames": true, "noFallthroughCasesInSwitch": true, "module": "esnext", "moduleResolution": "node", "resolveJsonModule": true, "isolatedModules": true, "noEmit": false, "jsx": "react-jsx" }, "include": ["src"] } Most important thing to consider is ModuleFederationPlugin. We specify name of the module and remotes we receive from outside of the project. And set shared dependencies for eager consumption.
Don't mess up remote names. If the names are set incorrectly project won't compile.
Final step is to edit index.html.
<html> <head> <script src="http://localhost:3001/remoteEntry.js"></script> <script src="http://localhost:3002/remoteEntry.js"></script> </head> <body> <div id="root"></div> </body> </html> Here, we add remotes with corresponding ports.
Now our container app is ready we need setup app-1 and app-2, and expose <Counter /> components. Steps are pretty much the same, we'll setup bootstrap.tsx and webpack.config.js.
There are only minor changes in webpack config.
App-1
Project Structure
├─ package.json ├─ public │ └─ index.html ├─ README.md ├─ src │ ├─ App.tsx │ ├─ bootstrap.tsx │ ├─ components │ │ └─ CounterAppOne.tsx │ └─ index.ts ├─ tsconfig.json ├─ webpack.config.js ├─ webpack.prod.js └─ yarn.lock Let's add our dependencies
npx create-react-app app-1 --template typescript yarn add html-webpack-plugin serve ts-loader webpack webpack-cli webpack-dev-server Just like we did in Container app we'll setup bootstrap.tsx, index.ts and app.tsx.
bootstrap.tsx
import App from './App'; import React from 'react'; import ReactDOM from 'react-dom'; ReactDOM.render(<App />, document.getElementById('root')); And add those into index.ts
index.ts
import('./bootstrap'); export {}; And, finally add those into app.tsx for future use. We will discuss them later.
app.tsx
import React from 'react'; import CounterAppOne from './components/CounterAppOne'; const App = () => ( <div style={{ margin: '20px' }}> <div>APP-1 - S4 </div> <div> <CounterAppOne /> </div> </div> ); export default App; Now we will create <Counter /> component which we will expose to container later in webpack config.
components > CounterAppOne.tsx
import React, { useState } from 'react'; const Counter = () => { const [count, setCount] = useState(0); return ( <div> <p> Add by one each click <strong>APP-1</strong> </p> <p>Your click count: {count} </p> <button onClick={() => setCount(count + 1)}>Click me</button> </div> ); }; export default Counter; We are pretty much done here, just need to add webpack configs.
const HtmlWebpackPlugin = require('html-webpack-plugin'); const { ModuleFederationPlugin } = require('webpack').container; const path = require('path'); const deps = require('./package.json').dependencies; module.exports = { entry: './src/index.ts', mode: 'development', devServer: { contentBase: path.join(__dirname, 'dist'), port: 3001, }, output: { publicPath: 'http://localhost:3001/', }, resolve: { extensions: ['.ts', '.tsx', '.js'], }, module: { rules: [ { test: /.(js|jsx|tsx|ts)$/, loader: 'ts-loader', exclude: /node_modules/, }, ], }, plugins: [ new ModuleFederationPlugin({ name: 'app1', library: { type: 'var', name: 'app1' }, filename: 'remoteEntry.js', exposes: { // expose each component './CounterAppOne': './src/components/CounterAppOne', }, shared: { ...deps, react: { singleton: true, eager: true, requiredVersion: deps.react }, 'react-dom': { singleton: true, eager: true, requiredVersion: deps['react-dom'], }, }, }), new HtmlWebpackPlugin({ template: './public/index.html', }), ], }; Update your package.json scripts as follows:
"scripts": { "start": "webpack serve --open", "build": "webpack --config webpack.prod.js", "serve": "serve dist -p 3001", "clean": "rm -rf dist" } Update your tsconfig as follows:
{ "compilerOptions": { "target": "es5", "lib": ["dom", "dom.iterable", "esnext"], "allowJs": true, "skipLibCheck": true, "esModuleInterop": true, "allowSyntheticDefaultImports": true, "strict": true, "forceConsistentCasingInFileNames": true, "noFallthroughCasesInSwitch": true, "module": "esnext", "moduleResolution": "node", "resolveJsonModule": true, "isolatedModules": true, "noEmit": false, "jsx": "react-jsx" }, "include": ["src"] } Edit index.html.
<html> <head> </head> <body> <div id="root"></div> </body> </html> This config has some differences. We set port differently, exposed our app instead of remoting it, and we have a thing called filename where expose our
module to different modules. Remember that we add <script src="http://localhost:3001/remoteEntry.js"></script> to our container index.html. This is where
container will look up for app-1.
Important things here:
- name: 'app1'
- filename: 'remoteEntry.js'
- expose
Exposing the wrong path very likely to cause a failure at compile time. Also settting up wrong name will cause a problem, because container is looking for app-1 if it can't
find it, it will fail.
App-2
Project Structure
├─ package.json ├─ public │ └─ index.html ├─ README.md ├─ src │ ├─ App.tsx │ ├─ bootstrap.tsx │ ├─ components │ │ └─ CounterAppTwo.tsx │ └─ index.ts ├─ tsconfig.json ├─ webpack.config.js ├─ webpack.prod.js └─ yarn.lock App-2 is pretty much the same. Create a new react project do all the thing above and just add <CounterAppTwo /> and webpack config.
components > CounterAppTwo
import React, { useState } from 'react'; const Counter = () => { const [count, setCount] = useState(1); return ( <div> <p> Multiply by two each click <strong>APP-2</strong> </p> <p>Your click count: {count}</p> <button onClick={() => setCount((prevState) => prevState * 2)}>Click me</button> </div> ); }; export default Counter; webpack.config.js
const HtmlWebpackPlugin = require('html-webpack-plugin'); const { ModuleFederationPlugin } = require('webpack').container; const path = require('path'); const deps = require('./package.json').dependencies; module.exports = { entry: './src/index.ts', mode: 'development', devServer: { contentBase: path.join(__dirname, 'dist'), port: 3002, }, output: { publicPath: 'http://localhost:3002/', }, resolve: { extensions: ['.ts', '.tsx', '.js'], }, module: { rules: [ { test: /.(js|jsx|tsx|ts)$/, loader: 'ts-loader', exclude: /node_modules/, }, ], }, plugins: [ new ModuleFederationPlugin({ name: 'app2', library: { type: 'var', name: 'app2' }, filename: 'remoteEntry.js', exposes: { // expose each component './CounterAppTwo': './src/components/CounterAppTwo', }, shared: { ...deps, react: { singleton: true, eager: true, requiredVersion: deps.react }, 'react-dom': { singleton: true, eager: true, requiredVersion: deps['react-dom'], }, }, }), new HtmlWebpackPlugin({ template: './public/index.html', }), ], }; Update your package.json scripts as follows:
"scripts": { "start": "webpack serve --open", "build": "webpack --config webpack.prod.js", "serve": "serve dist -p 3002", "clean": "rm -rf dist" } Update your tsconfig as follows:
{ "compilerOptions": { "target": "es5", "lib": ["dom", "dom.iterable", "esnext"], "allowJs": true, "skipLibCheck": true, "esModuleInterop": true, "allowSyntheticDefaultImports": true, "strict": true, "forceConsistentCasingInFileNames": true, "noFallthroughCasesInSwitch": true, "module": "esnext", "moduleResolution": "node", "resolveJsonModule": true, "isolatedModules": true, "noEmit": false, "jsx": "react-jsx" }, "include": ["src"] } Edit index.html.
<html> <head> </head> <body> <div id="root"></div> </body> </html> Now go to each project and run yarn start and navigate to localhost:3000. If you head over to sources tab in your
developer console, you'll see that each app comes from different port.
Roundup
Pros
- Easier to maintain
- Easier to test
- Independent deploy
- Increases scalability of the teams
Cons
- Requires lots of configuration
- If one of the projects crashes may affect other micro-frontends as well
- Having multiple projects run on the background for the development
In essence, it's pretty easy, bunch of apps getting together in a same website and being served from different servers. If you are dealing with huge codebases, it's a fantastic technology
to keep in your arsenal. It will feel like a breeze to decouple your huge components into little apps. I hope I encouraged you to give micro-frontends a try.