# Implementing micro frontend

## Stack

* VueJS -> container
* ReactJS + web component -> component
* Rollup -> bundling component

## ReactJS + Web component

* Here is the react component

{% code title="Count/index.js" %}
```javascript
import React from 'react'
import styles from "./count.module.scss";
const Count = ({count}) => {
  return (
    <div className={styles.text}>{count}</div>
  )
}

export default Count
```
{% endcode %}

{% code title="Count/count.module.scss" %}
```sass
.text{
    color: aquamarine;
}
```
{% endcode %}

* Here is the script of web component which is wrapper of react component

{% code title="Count/count.js" %}
```javascript
import ReactDOM from 'react-dom/client';
import Count from '.';

class CountElement extends HTMLElement {

    get count(){
        return this.getAttribute("count");
    }

    set count(val){
        this.setAttribute("count",val);
    }

    connectedCallback() {
        this.attachShadow({mode: 'open'});
        let link = document.createElement('link');
        link.setAttribute('rel', 'stylesheet');
        link.setAttribute('href', 'http://localhost:3000/component.css');
        this.shadowRoot.appendChild(link);
        const mountPoint = document.createElement("div");
        this.shadowRoot.appendChild(mountPoint);
        const root = ReactDOM.createRoot(mountPoint);
        root.render(<Count count={this.count}/>);
    }

}
window.customElements.define("count-display", CountElement);
```
{% endcode %}

{% code title="CountButton/countButton.js" %}
```javascript
import ReactDOM from 'react-dom/client';
import CountButton from '.';

class CountButtonElement extends HTMLElement {
    connectedCallback() {
        this.attachShadow({mode: 'open'});
        let link = document.createElement('link');
        link.setAttribute('rel', 'stylesheet');
        link.setAttribute('href', 'http://localhost:3000/component.css');
        this.shadowRoot.appendChild(link);
        const mountPoint = document.createElement("div");
        this.shadowRoot.appendChild(mountPoint);
        const root = ReactDOM.createRoot(mountPoint);
       
       // emit the event with custom name
        const event = new CustomEvent("onAddCount",{ 
            // allow event buddle up to parent
            buddles: true, 
            // allow event to propagate across shadow boundaries
            composed:true
        })

        root.render(<CountButton onAddCount={()=>{
            document.dispatchEvent(event);
        }} />);
    }
}

window.customElements.define("count-button", CountButtonElement);
```
{% endcode %}

* Here is the main target bundling file

{% code title="component.js" %}
```javascript
import "./Count/count";
import "./CountButton/countButton";
```
{% endcode %}

* Here is the rollup file, to bundle css and web component js file as a output

{% code title="rollup.config.js" %}
```javascript
import resolve from "@rollup/plugin-node-resolve";
import { terser } from "rollup-plugin-terser";
import postcss from 'rollup-plugin-postcss';
import commonjs from '@rollup/plugin-commonjs';
import babel from '@rollup/plugin-babel';
import externalGlobals from "rollup-plugin-external-globals";

// hard node env to production for bundled js file
const Global = `var process = {
    env: {
      NODE_ENV: 'production'
    }
  }`
// eslint-disable-next-line import/no-anonymous-default-export
export default {
    input: "src/component/component.js",
    output: {
        file: "public/component.js",
        format: "esm",
        banner: Global
    },
    // prevent bundling with react 
    external: ["react","react-dom", "react-scripts"],
    plugins: [
        resolve(),
        babel({
            presets: ["@babel/preset-react"],
        }),
        commonjs(),
        // reduce the bundle size
        terser(),
        // support sass, bundle multiple sass files into single css file
        postcss({
            extract: true,
            modules: true,
            use: ['sass'],
        }),
        // make sure react is injected from the script of vue container
        externalGlobals({
            react: "React",
            "react-dom": "ReactDOM",
        })
        
    ],
}
```
{% endcode %}

* Here is the package.json

{% code title="package.json" %}
```json
{
  "name": "react-microfrontend",
  "version": "0.1.0",
  "private": true,
  "dependencies": {
    "@testing-library/jest-dom": "^5.16.4",
    "@testing-library/react": "^13.3.0",
    "@testing-library/user-event": "^13.5.0",
    "react": "^18.2.0",
    "react-dom": "^18.2.0",
    "react-scripts": "5.0.1",
    "web-vitals": "^2.1.4"
  },
  "devDependencies": {
    "@babel/preset-react": "^7.18.6",
    "@rollup/plugin-babel": "^5.3.1",
    "@rollup/plugin-commonjs": "^22.0.0",
    "@rollup/plugin-node-resolve": "^13.3.0",
    "node-sass": "^7.0.1",
    "postcss": "^8.4.14",
    "rollup": "^2.75.7",
    "rollup-plugin-dts": "^4.2.2",
    "rollup-plugin-external-globals": "^0.6.1",
    "rollup-plugin-peer-deps-external": "^2.2.4",
    "rollup-plugin-postcss": "^4.0.2",
    "rollup-plugin-sass": "^1.2.12",
    "rollup-plugin-terser": "^7.0.2",
    "sass": "^1.53.0"
  },
  "scripts": {
    "start": "react-scripts start",
    "build": "react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject",
    "build:rollup": "rollup -c"
  },
  "eslintConfig": {
    "extends": [
      "react-app",
      "react-app/jest"
    ]
  },
  "browserslist": {
    "production": [
      ">0.2%",
      "not dead",
      "not op_mini all"
    ],
    "development": [
      "last 1 chrome version",
      "last 1 firefox version",
      "last 1 safari version"
    ]
  }
}
```
{% endcode %}

## VueJS

* Here is the public html file which is injected the output script file from react repo and react script file

{% code title="public/index.html" %}
```html
<!DOCTYPE html>
<html lang="">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <link rel="icon" href="<%= BASE_URL %>favicon.ico">
    <script src="https://unpkg.com/react@18/umd/react.development.js" crossorigin ></script>
    <script src="https://unpkg.com/react-dom@18/umd/react-dom.development.js" crossorigin ></script>
    <script type="module" src="http://localhost:3000/component.js" defer></script>
    <title><%= htmlWebpackPlugin.options.title %></title>
  </head>
  <body>
    <noscript>
      <strong>We're sorry but <%= htmlWebpackPlugin.options.title %> doesn't work properly without JavaScript enabled. Please enable it to continue.</strong>
    </noscript>
    <div id="app"></div>
    <!-- built files will be auto injected -->
  </body>
</html>
```
{% endcode %}

* Here is main app file of vue

{% code title="App.vue" %}
```javascript
<template>
  <count-display :count="count" :key="count" />
  <count-button  />
</template>

<script>

export default {
  name: 'App',
  components: {
  },
  data() {
    return {
      count: 0
    }
  },
   methods: {
    increment() {
      this.count++
    }
  },
  mounted(){
    document.addEventListener("onAddCount", this.increment);
  }
}
</script>

<style>
</style>
```
{% endcode %}

## Result

![](https://1374779285-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MFW3x2aqEO8GF2kr3VU%2Fuploads%2FUxcs8mpJBKOi6aYV8t09%2Fimage.png?alt=media\&token=1ddee436-71ba-4e38-91bc-17dd166137a9)

{% embed url="https://github.com/headshootcheng/vue-container" %}

{% embed url="https://github.com/headshootcheng/react-microfrontend" %}
