A Comprehensive Guide to Mastering Angular Components

Introduction

Angular is a popular open-source web application framework developed by Google. It is designed to make both the development and testing of applications easier. A fundamental part of any Angular application are the Angular components. They are the building blocks of an Angular application. This blog post will dive deep into Angular components, covering topics from basics, creation via CLI, to more advanced topics.

Basics of Angular Components

What is a Component?

In Angular, a component controls a part of the app's user interface (UI) that is displayed on a browser page. A component is composed of three things:

Template : This is the HTML markup that defines the structure and UI of the component.
Class : This is a TypeScript class that implements the component's functionality.
Metadata : This is information provided by the decorator that specifies how the component should be processed, instantiated, and used at runtime.

Component Decorator

Each component class is decorated with @Component decorator. The @Component decorator identifies the class as a component class and specifies its metadata.

import { Component } from '@angular/core'; 
    
@Component({ 
    selector: 'app-root', 
    templateUrl: './app.component.html', 
    styleUrls: ['./app.component.css'] 
}) 

export class AppComponent { 
    title = 'My Angular App'; 
    }

In the example above:

selector : Defines the HTML tag that will be associated with this component. In this case, <app-root></app-root> tag will be associated with AppComponent .
templateUrl : Specifies the location of the component's template file.
styleUrls : Specifies the location of the component's CSS files.

Creating a Component via Angular CLI

Angular CLI is a command-line interface tool that can be used to create new projects, generate application and library code, and perform a variety of ongoing development tasks such as testing, bundling, and deployment.

Installing Angular CLI

To install Angular CLI, open a terminal and run the following command:

npm install -g @angular/cli

Generating a New Component

To generate a new component, navigate to your Angular project directory and run the following command:

ng generate component my-new-component

Or you can use the shorthand:

ng g c my-new-component

This will create a new directory called my-new-component with four files:

my-new-component.component.ts : This is the TypeScript file containing the component class.
my-new-component.component.html : This is the HTML template file.
my-new-component.component.css : This is the CSS file for the component.
my-new-component.component.spec.ts : This is the testing file for the component.

Angular CLI will also update the app.module.ts file to declare the new component.

Using a Component

To use a component, you need to do three things:

Declare the Component : The component should be declared in an Angular module.
Specify the Component in a Template : Use the component's selector to embed it into an Angular template.
Configure the Component : Configure the component with required inputs and listen for desired outputs.

Declaring a Component

Every Angular component must be declared in an Angular module. By default, the Angular CLI declares the component in the app.module.ts file.

import { BrowserModule } from '@angular/platform-browser'; import { NgModule } from '@angular/core'; import { AppComponent } from './app.component'; import { MyNewComponentComponent } from './my-new-component/my-new-component.component'; @NgModule({ declarations: [ AppComponent, MyNewComponentComponent ], imports: [ BrowserModule ], providers: [], bootstrap: [AppComponent] }) export class AppModule { }

In the example above, the MyNewComponentComponent is declared in the declarations array of the AppModule .

Specifying the Component in a Template

To use the component in a template, simply use its selector. For example, if you want to use MyNewComponentComponent in AppComponent , you can update the app.component.html file like this:

<h1>{ { title } }</h1> <app-my-new-component></app-my-new-component>

Configuring the Component

Components can have @Input and @Output properties. @Input properties are used to pass data into a component, and @Output properties are used to pass data out of a component.

For example, if MyNewComponentComponent has an input property called name and an output property called nameChange , you can configure the component like this:

<app-my-new-component [name]="currentName" (nameChange)="currentName=$event"></app-my-new-component>

In this example, currentName is a property of the parent component, and $event is the data emitted by the nameChange event.

Conclusion

Angular components are the building blocks of any Angular application. Understanding how to create, use, and configure components is essential for developing Angular applications. This blog post covered the basics of Angular components, how to create a component using Angular CLI, and how to use and configure a component. With this knowledge, you can start creating more complex Angular applications. Happy coding!