Introduction to Angular Components and How to Implement Them?

Unlock the power of Angular by mastering its building blocks-Angular components! This tutorial will take you through the core of Angular development, starting with an introduction to Angular components. You'll discover how these dynamic, reusable pieces of code bring your applications to life. By the end, you'll understand the fundamentals and learn how to implement them like a pro, making your Angular apps more efficient and scalable.

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What are Angular Components?

Angular components are the building blocks of a UI in an Angular application. These components are associated with a template and are a subset of directives.

The above image shows the classification tree structure. A root component, the AppComponent, branches out into other components, creating a hierarchy.

Here are some of the features of Angular Component: 

• Components are typically custom HTML elements, and each of these elements can instantiate only one component.
• A TypeScript class is used to create a component. This class is then decorated with the “@Component” decorator.
• The decorator accepts a metadata object that gives information about the component.
• A component must belong to the NgModule for it to be usable by another component or application.
• Components control their runtime behavior by implementing Life-Cycle hooks.

The above image shows an AppComponent, a pure TypeScript class decorated with the “@Component” decorator. The metadata object provides properties like selector, templateUrl, and so on—the templateUrL points to an HTML file that defines what you see on your application.

In the index.html file, the <app-root> tag corresponds to the component’s selector. By doing so, Angular will inject the corresponding template for the element.

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Creating Your First Angular Component

• Angular CLI is used to create an Angular component. In the terminal, type in the command,

  ng g c component-name

• This will create a folder named component-name with four files. 

You’ll also receive a message: 

The update message indicates that the component created is included in the declarations array of the main component.

Angular needs to know which component to run next and its features. For that, some metadata is created. The following section addresses the component metadata.

Component Decorator Metadata

As mentioned earlier, the @Component decorator accepts a metadata object that provides information about the component. Here’s a list of properties of the metadata object:

@Component({
  selector: 'app-root',
  template: `<h1>Hello! Welcome</h1>`,
  templateUrl: './app.component.html',
  styles: [`
    h3{
      color: blue;
    }
  `],
  styleUrls: ['./app.component.css']

Selector

It is the CSS selector that identifies this component in a template. This corresponds to the HTML tag that is included in the parent component. You can create your HTML tag. However, the same has to be included in the parent component.

Template

It is an inline-defined template for the view. The template can define some markup, typically including headings or paragraphs displayed on the UI.

templateUrl

It is the URL for the external file containing the template for the view.

Styles

These are inline-defined styles to be applied to the component’s view.

styleUrls

List of URLs to stylesheets to be applied to the component’s view. 

Providers

It is an array where certain services can be registered for the component.

Animations

Animations can be listed for the components.

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Demo: Creating an Angular Component

Step 1: Create a folder in your application to store all your components.

ng g c components/new-component

Please observe that the extension .component is appended to indicate it is a component.

Step 2: Open the new-component.component.html file within the component to type in whatever you’d like to see on the browser.

<h1>Hey! I'm the first component</h1>

Step 3: In the new-component.component.ts file, copy the selector property to incorporate it in the app.component.html file.

@Component({
  selector: 'app-new-component',
  templateUrl: './new-component.component.html',
  styleUrls: ['./new-component.component.css']
})

Define the custom HTML tag in the app.component.html, the root component. This indicates that the created component is being incorporated into the final render.

<h1>Welcome to this tutorial on Angular Components</h1>
<app-new-component></app-new-component>
You can also define any styling conventions for the component in the CSS file. 
h1 {
    text-align: center;
}

Once you execute the ng serve command, the output looks like this. 

You can create multiple components and define the tags in the app component. The components are executed sequentially.

We have created another component within which we’ve embedded the Simplilearn logo.

<h1>This is the image component</h1>
    <img src= "assets/Angular_logo.png" class="center">
I’ve also specified styling conventions in its corresponding CSS file. 
h1 {
    color: green;
    text-align: center;
}
.center {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 50%;
  }

The final output looks like this, 

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Next Steps

This tutorial briefly introduced Angular components, giving you a glimpse into their role in front-end development. To fully master Angular and elevate your coding career, pursuing a certification is highly recommended. Simplilearn's Full Stack Developer - MERN Stack program is designed to make you an expert in front-end web development with Angular. You'll dive deep into essential concepts such as single-page application development, dependency injection, TypeScript, components, and directives. Through hands-on projects, including building a real-time application, you'll gain practical experience to solidify your skills.

FAQs

1. What is the difference between Angular service and component?

An Angular component is responsible for the application's user interface and behavior, including displaying data and handling user input. In contrast, an Angular service is a class that shares data and functionality across different components. Services are typically used for tasks like fetching data from an API, business logic, or shared utilities, while components handle the presentation and user interaction.

2. What are Angular modules and components?

An Angular module is a container for a group of related components, services, directives, and pipes that form a functional unit within the application. Modules help organize an application into cohesive blocks of functionality. On the other hand, an Angular component is a building block of the UI, consisting of a TypeScript class, an HTML template, and optional CSS styles. It is responsible for rendering a view and handling user interaction.

3. How to add a component in Angular?

To add an Angular component, use the Angular CLI command: ng generate component <component-name> or ng g c <component-name>. This command creates a new directory with the component’s TypeScript, HTML, and CSS files. Once created, you must declare the component in the appropriate Angular module's @NgModule decorator under the declarations array to use it in your application.

4. What is lazy loading in Angular?

Lazy loading in Angular is a technique that loads modules only when needed rather than at the start of the application. This improves performance by reducing the initial load time. To implement lazy loading, define routes with loadChildren in the routing module, pointing to the module you want to load lazily. This ensures the module is loaded only when the user navigates to the corresponding route.