Angular is a popular front-end web development framework that provides a robust set of features and tools to build scalable web applications. However, building scalable Angular applications can be a daunting task. In this article, we will discuss 10 best practices for building scalable Angular applications, along with code examples, explanations, and examples of bad practices to avoid.
1. Use a Modular Architecture
Modularity is crucial when building scalable Angular applications. You can organize your code into modules that represent different features or sections of your application. Each module should have a clear responsibility and a defined interface. This approach makes it easier to manage complexity and enables code reuse. Below is an example of a simple Angular module:
import { NgModule } from '@angular/core';
import { SharedModule } from '../shared/shared.module';
import { ProductsRoutingModule } from './products-routing.module';
import { ProductListComponent } from './product-list.component';
import { ProductDetailComponent } from './product-detail.component';
@NgModule({
declarations: [
ProductListComponent,
ProductDetailComponent
],
imports: [
SharedModule,
ProductsRoutingModule
],
exports: [
ProductListComponent,
ProductDetailComponent
]
})
export class ProductsModule { }
In this example, the ProductsModule is exporting both the ProductListComponent and the ProductDetailComponent. These components are closely related and serve a common purpose, which is to display a list of products and their details.
The ProductsModule is also importing the SharedModule, which contains any commonly used components, pipes, or directives that are used across multiple modules in the application. Additionally, it’s importing a routing module, ProductsRoutingModule, which is responsible for defining the routes and handling navigation for these components.
By following these best practices, the ProductsModule is well-organized, maintainable, and performant. It’s also reusable in other parts of the application, making it a valuable asset to the overall architecture.
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { ProductService } from './product.service';
import { ProductListComponent } from './product-list.component';
@NgModule({
declarations: [
ProductListComponent
],
imports: [
FormsModule // Not used
],
providers: [
ProductService
]
})
export class ProductsModule { }
In this example, the ProductsModule violates some best practices in a few ways:
- The module is importing FormsModule, which is a module used for template-driven forms in Angular. However, this module is not necessary for the ProductListComponent, which is not using template-driven forms. This can add unnecessary code and bloat to the application.
- The module is only declaring and exporting one component, which is the ProductListComponent. This may be acceptable in some cases, as I mentioned earlier, but in this case, it’s not clear if this module will be extended with other components in the future.
- The module is providing the ProductService, which is a service that is used to retrieve data for the ProductListComponent. However, it’s not clear if this service will be used elsewhere in the application or if it’s specific to this module.
Overall, this example violates best practices related to code organization, dependency management, and maintainability. By following best practices, such as properly importing only necessary modules, exporting all relevant components, and clearly defining the scope of services, we can improve the performance and maintainability of our application.
2. Use Reactive Programming
Reactive programming is a powerful paradigm that can help you build scalable Angular applications. Reactive programming is all about handling streams of data and events, and it can make your code more concise, efficient, and responsive. Angular provides a powerful set of reactive programming tools, such as RxJS and the Angular Forms API. Here’s an example of a simple reactive component:
import { Component } from '@angular/core';
import { FormControl } from '@angular/forms';
import { debounceTime, distinctUntilChanged, switchMap } from 'rxjs/operators';
import { ApiService } from './api.service';
@Component({
selector: 'app-search',
template: `
<input type="text" [formControl]="search" />
<ul>
<li *ngFor="let item of items">{{ item }}</li>
</ul>
`
})
export class SearchComponent {
search = new FormControl();
items: string[] = [];
constructor(private apiService: ApiService) {
this.search.valueChanges.pipe(
debounceTime(300),
distinctUntilChanged(),
switchMap((query: string) => this.apiService.search(query))
).subscribe((result: string[]) => {
this.items = result;
});
}
}
This code defines an Angular component called SearchComponent. This component contains a search input field and a list of search results that are displayed as a list of items. When the user types into the search input field, the component retrieves data from an external API using an ApiService and displays the results in the list.
Here are the steps that the code follows:
This code defines an Angular component called SearchComponent. This component contains a search input field and a list of search results that are displayed as a list of items. When the user types into the search input field, the component retrieves data from an external API using an ApiService and displays the results in the list.
Here are the steps that the code follows:
- It imports several modules from Angular and RxJS, including Component, FormControl, debounceTime, distinctUntilChanged, and switchMap.
- It defines the SearchComponent class and decorates it with the @Component decorator. The decorator provides metadata about the component, such as the selector, which is used to identify the component in the HTML template.
- The component defines a FormControl called search and an array of strings called items.
- The constructor function sets up an Observable that listens to changes in the search FormControl. It uses several RxJS operators to filter and debounce the user input and to perform a search query using the ApiService.
- When the search query returns results, the items array is updated, and the component re-renders the list of items in the template.
Overall, this code demonstrates how to use Reactive Forms in Angular to build a dynamic search feature that retrieves data from an external API. By leveraging the power of RxJS observables and Angular’s component lifecycle hooks, the code provides a responsive and efficient user experience.
3. Use Lazy Loading
Lazy loading is a technique that can improve the performance of your Angular application by loading modules only when they are needed. This approach can reduce the initial load time of your application and improve the overall user experience. Here’s an example of how to use lazy loading in Angular:
const routes: Routes = [
{ path: '', component: HomeComponent },
{ path: 'about', loadChildren: () => import('./about/about.module').then(m => m.AboutModule) }
];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }
In this code, we define the application routes using the Routes interface provided by the @angular/router package. The routes are defined in a constant variable named routes. There are two routes defined:
- The first route is the default route (‘’) that points to the HomeComponent.
- The second route (‘about’) is a lazy-loaded route that loads a feature module named AboutModule when the user navigates to it. This is accomplished by setting the loadChildren property of the route to a function that returns a Promise that resolves to the AboutModule. The
import()function is used to dynamically load the module at runtime, and thethen()function is used to return the AboutModule.
The lazy-loading mechanism in Angular allows us to split our application into smaller feature modules that can be loaded on demand as the user navigates through the application. This can significantly reduce the initial load time of our application and improve the performance by only loading the required modules when needed. In the example above, the AboutModule is only loaded when the user navigates to the ‘about’ route. This means that the AboutModule and its dependencies are not loaded until they are actually needed, making our application more efficient and responsive.
4. Use Ahead-of-Time Compilation
Ahead-of-time (AOT) compilation is a technique that can improve the performance and security of your Angular application. AOT compilation compiles your Angular templates and TypeScript code into efficient JavaScript code during the build process, which can improve the startup time of your application and reduce the risk of template injection attacks. Here’s an example of how to enable AOT compilation in Angular:
ng build --prod --aot
5. Use Change Detection Strategy OnPush
Change detection is a core concept in Angular that can impact the performance of your application. Change detection is the process of detecting changes in your application’s data and updating the view accordingly. By default, Angular uses a strategy called “Default” change detection, which can be resource-intensive. However, you can optimize your application’s performance by using the “OnPush” change detection strategy. The “OnPush” strategy detects changes only when the input properties of a component change or when an event is triggered. Here’s an example of how to use the “OnPush” change detection strategy:
import { Component, ChangeDetectionStrategy } from '@angular/core';
@Component({
selector: 'app-item',
template: `
<div>{{ item.name }}</div>
<div>{{ item.price | currency }}</div>
<button (click)="addToCart()">Add to Cart</button>
`,
changeDetection: ChangeDetectionStrategy.OnPush
})
export class ItemComponent {
@Input() item: Item;
constructor(private cartService: CartService) {}
addToCart() {
this.cartService.addItem(this.item);
}
}ty
6. Use Reactive Forms
Reactive Forms are a powerful tool for building complex forms in Angular. Reactive Forms allow you to handle form data in a reactive way and provide features such as validation, error handling, and dynamic form controls. Here’s an example of a simple Reactive Form:
import { Component } from '@angular/core';
import { FormGroup, FormBuilder, Validators } from '@angular/forms';
@Component({
selector: 'app-contact',
template: `
<form [formGroup]="contactForm" (ngSubmit)="submit()">
<input type="text" formControlName="name" />
<input type="email" formControlName="email" />
<textarea formControlName="message"></textarea>
<button type="submit">Send</button>
</form>
`
})
export class ContactComponent {
contactForm: FormGroup;
constructor(private formBuilder: FormBuilder, private apiService: ApiService) {
this.contactForm = this.formBuilder.group({
name: ['', Validators.required],
email: ['', [Validators.required, Validators.email]],
message: ['', Validators.required]
});
}
submit() {
if (this.contactForm.valid) {
this.apiService.sendMessage(this.contactForm.value).subscribe(() => {
this.contactForm.reset();
});
}
}
}
7. Use Smart and Dumb Components
In Angular, the concept of “smart” and “dumb” components is a pattern for structuring the application components. This pattern is also known as the “Container/Presentation” pattern.
A “smart” component, also known as a container component, is a component that has the responsibility of managing the state of the application and orchestrating the interactions between the components. A smart component is typically connected to a service or a store that manages the state of the application. It contains the business logic of the application and handles data fetching, transformation, and manipulation. Smart components are responsible for handling user interactions and propagating the state changes to the child components.
On the other hand, a “dumb” component, also known as a presentation component, is a component that has no knowledge of the application state and only receives data and events from the parent components through inputs and outputs. Dumb components are designed to be reusable and encapsulate the presentation logic of the application. They have a simple API and are easy to test and maintain.
The separation of smart and dumb components helps to improve the overall organization and maintainability of the application. Smart components are responsible for managing the application state, while dumb components are responsible for displaying the data and interacting with the user. This separation allows for a better separation of concerns and makes it easier to test and maintain the application.
The following example demonstrates the smart and dumb component pattern in Angular:
import { Component } from '@angular/core';
import { Observable } from 'rxjs';
import { Todo } from '../models/todo';
import { TodoService } from '../services/todo.service';
@Component({
selector: 'app-todo-list-container',
template: `
<app-todo-list [todos]="todos$ | async"></app-todo-list>
`
})
export class TodoListContainerComponent {
todos$: Observable<Todo[]>;
constructor(private todoService: TodoService) {
this.todos$ = this.todoService.getTodos();
}
}
@Component({
selector: 'app-todo-list',
template: `
<ul>
<li *ngFor="let todo of todos">
{{ todo.title }}
</li>
</ul>
`
})
export class TodoListComponent {
@Input() todos: Todo[];
}
In this example, we have two components: TodoListContainerComponent and TodoListComponent.
The TodoListContainerComponent is the smart component, which is responsible for managing the application state. It uses a TodoService to fetch the list of todos and then passes the list to the TodoListComponent as an input property.
The TodoListComponent is the dumb component, which is responsible for displaying the data. It receives the list of todos as an input property and uses *ngFor to render each todo item.
By using the smart and dumb component pattern, we can improve the separation of concerns and make the code more modular, reusable, and easier to test and maintain.
8. Use Angular Material for UI components
Angular Material is a UI component library for Angular applications that provides a set of pre-built and customizable UI components based on Google’s Material Design guidelines. Material Design is a design language developed by Google, which emphasizes on using clean and modern design principles such as minimalism, simplicity, and consistent use of color and typography.
Using Angular Material in your application not only saves time and effort in designing and building UI components from scratch but also ensures that your application has a modern and consistent look and feel. Additionally, Angular Material is responsive and accessible by default, which means your application will work seamlessly on different devices and assistive technologies.
Here are some useful links to get started with Angular Material:
- Angular Material official website: https://material.angular.io/
- Getting started with Angular Material: https://material.angular.io/guide/getting-started
- Angular Material UI components: https://material.angular.io/components/overview
- Angular Material theming: https://material.angular.io/guide/theming
- Angular Material examples and demos: https://material.angular.io/components/categories
By using Angular Material, you can quickly add professional and consistent UI components to your Angular application, which not only saves development time but also enhances the user experience.
9. Write unit tests
Writing unit tests is an essential practice when building scalable Angular applications. Unit testing involves writing test cases for individual units of code, such as components, services, and pipes, to ensure that they work as expected and meet the requirements. Unit tests can detect bugs early in the development process, ensure that code changes do not break existing functionality, and make code more maintainable and scalable.
Angular provides a built-in testing framework, which uses tools like Jasmine and Karma to write and run tests. Jasmine is a popular testing framework for JavaScript applications that provides a clean syntax for writing test cases and assertions. Karma is a test runner that automates the execution of test cases and generates reports.
Here’s an example of a unit test for an Angular component using Jasmine and Karma:
import { TestBed, ComponentFixture } from '@angular/core/testing';
import { By } from '@angular/platform-browser';
import { Component } from '@angular/core';
import { MyComponent } from './my.component';
describe('MyComponent', () => {
let component: MyComponent;
let fixture: ComponentFixture<MyComponent>;
beforeEach(async () => {
await TestBed.configureTestingModule({
declarations: [ MyComponent ]
})
.compileComponents();
});
beforeEach(() => {
fixture = TestBed.createComponent(MyComponent);
component = fixture.componentInstance;
fixture.detectChanges();
});
it('should create', () => {
expect(component).toBeTruthy();
});
it('should display the correct title', () => {
const title = 'My Title';
component.title = title;
fixture.detectChanges();
const titleElement = fixture.debugElement.query(By.css('h1'));
expect(titleElement.nativeElement.textContent).toContain(title);
});
});
Here’s the corresponding HTML template for MyComponent:
@Component({
template: `
<h1>{{ title }}</h1>
`
})
export class MyComponent {
title: string;
}
In this example, we have a component called MyComponent with a simple template that displays a title. We use TestBed and ComponentFixture from @angular/core/testing to create and interact with an instance of the component in our tests.
The beforeEach block with TestBed.configureTestingModule sets up the testing module with the component we want to test.
The beforeEach block with TestBed.createComponent creates a fixture for the component and retrieves an instance of the component.
The it block with expect(component).toBeTruthy() checks that the component was created successfully.
The it block with expect(titleElement.nativeElement.textContent).toContain(title) checks that the title element in the template contains the correct title.
These tests ensure that our component behaves as expected and that changes to the component’s code don’t introduce unintended side effects.
10. Use Angular CLI to generate and manage your application
Angular CLI is a powerful tool that simplifies the process of creating, managing, and building Angular applications. It provides a set of commands that allow you to quickly create components, services, modules, and other parts of your application. Additionally, it takes care of many configuration and build tasks, such as optimizing your application for production, running tests, and generating documentation.
By using Angular CLI, you can save time and effort in setting up and maintaining your application. It also ensures that your application adheres to best practices and conventions that are recommended by the Angular team. Overall, using Angular CLI can greatly enhance the scalability, maintainability, and quality of your Angular application.
Here are some examples of Angular CLI commands:
ng new my-app: Generates a new Angular application with the default project structure and configuration.ng generate component my-component: Generates a new component with the specified name and adds it to the app module.ng generate service my-service: Generates a new service with the specified name and adds it to the app module.ng generate module my-module: Generates a new module with the specified name and adds it to the app module.ng test: Runs all unit tests in the application using Karma and Jasmine.ng build: Builds the application for production and generates a set of optimized static files in thedist/directory.ng serve: Starts a development server that serves the application and automatically reloads it when changes are made.
These are just a few examples of the many commands available in Angular CLI. You can find more information on how to use Angular CLI and its commands in the official documentation: https://angular.io/cli
In conclusion
Following these best practices can help you build scalable and maintainable Angular applications. Use a modular approach to keep your code organized and decoupled, lazy load your modules to reduce initial load time, write reusable and testable code, and use Angular Material for UI components. Additionally, take advantage of Angular CLI commands to streamline your development workflow and use Git for version control.
Further reading:
- Angular Style Guide: https://angular.io/guide/styleguide
- Angular Material: https://material.angular.io/
- Angular CLI: https://angular.io/cli
- Git: https://git-scm.com/
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