Beginner's Guide To Micro Front-Ends Using Angular Elements

Front-end development has grown so much over the last decade from pure HTML and CSS design to topics such as high interactivity, accessibility, testability, and security. In order to meet these needs, most application teams have made distinctions between backend and front-end development teams.

In addition to that, the application functionality grows steadily and, at a certain point, it becomes impractical to have multiple teams collaborate on a single code base.

The term "Micro Front-ends" has been a buzzword for breaking up growing front-end code into easy-to-maintain parts. The front-end is divided into its multiple functions or parts. These parts are implemented and deployed by independent teams. This increases the testability, reusability, and offers the possibility to select different technologies for each micro front-end.

I will stop at this point and, without further ado, let's build sample micro front-ends using Angular elements.

Building Micro Front-Ends

We will build a sample travel booking system in this article. Let's spin up two Angular projects using CLI: travel-booking and flight-booking.

We will need a few dependencies to build and run Angular custom elements. Install the following dependencies inside flight-booking using following commands.

ng add @angular/elements 
ng add ngx-build-plus

These dependencies can also be installed via npm. @angular/elements provides support for Angular elements. ngx-build-plus is a build tool for Angular which is an extension of Angular CLI.

Note: You may need to update the version for the document-register-element module to 1.8.1 in /flight-booking/package.json as described in this issue.

Let us also install the HTTP-server module inside the flight-booking project.

npm i -g http-server --save

Create a component booking in flight-booking/src/app/. Let's modify the component as follows:
flight-booking/src/app/booking/booking.component.html

<!--The content below is only a placeholder and can be replaced.-->

<div style="text-align:center">

  <a href="javascript:alert('Welcome to Flight Booking App!!');" style="font-size:25px;">{{ title }}</a>

</div>

flight-booking/src/app/booking/booking.component.ts

import { Component, OnInit } from '@angular/core';

@Component({

  selector: 'app-flight-booking',

  templateUrl: './booking.component.html',

  styleUrls: ['./booking.component.scss']

})

export class BookingComponent implements OnInit {

  title = 'Flight Booking App';

  constructor() { }

  ngOnInit() {

  }

Let's define the booking component as custom element in flight-booking/src/app/app.module.ts.

import { BrowserModule } from '@angular/platform-browser';

import { NgModule, Injector } from '@angular/core';

import { AppRoutingModule } from './app-routing.module';

import { AppComponent } from './app.component';

import { createCustomElement } from '@angular/elements';

import { BookingComponent } from './booking/booking.component';

@NgModule({

  declarations: [

    AppComponent,

    BookingComponent

  ],

  imports: [

    BrowserModule,

    AppRoutingModule

  ],

  providers: [],

  bootstrap: [],

  entryComponents: [

    BookingComponent

  ]

})

export class AppModule {

  constructor(private injector: Injector) {

  }

  ngDoBootstrap() {

    const myCustomElement = createCustomElement(BookingComponent, { injector: this.injector });

    customElements.define('app-flight-booking', myCustomElement);

  }

}

To build the project in a single JS file, we need to tell angular to use the ngx-build-plus module. Modify flight-booking/angular.json in three places as follows:

"architect": {  "build": {    "builder": "ngx-build-plus:build",  ....

"serve": {    "builder": "ngx-build-plus:dev-server",    ...

 "test": {    "builder": "ngx-build-plus:karma",

Running the Project

Run the following command to build the project into a single JS file.

ng build --prod --output-hashing none --single-bundle true

--output-hashing none will avoid hashing the file names.

--single-bundle true will bundle all the compiled files into a single JS file.

Start the server.

http-server ./dist/flight-booking -p 8081

Similarly, create another custom element, train-booking, and run the server with port 8082.

http-server ./dist/train-booking -p 8082

Wrapping a Custom Element

Let us include flight-booking and train-booking custom elements in travel-booking app. Modify /travel-booking/index.html as follows.

<!doctype html>

<html lang="en">

<head>

  <meta charset="utf-8">

  <title>TravelBooking</title>

  <base href="/">

  <meta name="viewport" content="width=device-width, initial-scale=1">

  <link rel="icon" type="image/x-icon" href="favicon.ico">

</head>

<body>

  <app-root></app-root>

  <div style="margin-bottom: 10px;" id="flight-booking-container"><app-flight-booking></app-flight-booking></div>

  <div id="train-booking-container"><app-train-booking></app-train-booking></div>

  <script src="https://cdnjs.cloudflare.com/ajax/libs/zone.js/0.9.1/zone.min.js"></script>

  <script src="https://cdnjs.cloudflare.com/ajax/libs/webcomponentsjs/2.2.10/custom-elements-es5-adapter.js"></script>

  <script type="text/javascript" src="http://localhost:8081/main.js"></script>

  <script type="text/javascript" src="http://localhost:8082/main.js"></script>

</body>

</html>

Here, Angular requires zones. and custom-elements-es5-adapter.js provides custom element support within the browser. We also included main.js from our custom elements.

Modify travel-booking/angular.json to override the default server port.

"serve": {

          "builder": "@angular-devkit/build-angular:dev-server",

          "options": {

            "browserTarget": "travel-booking:build",

            "port": 8080

          }

Running the Main Application

Run the application using ng serve. The final application will look like this:

Wrapping Up

Using simple examples, this article demonstrates how we can build a micro front-end architecture using Angular elements. I hope you enjoyed my article. Let me know your experiences if you are working with micro front-end architecture.