The Concepts of Angular Components -
Components are the most basic
building block of a UI in Angular applications and it controls views
(HTML/CSS). They also communicate with other components and services to bring
functionality to your applications.
Technically components are basically
TypeScript classes that interact with the HTML files of the components, which
get displayed on the browsers.
The component is the core
functionality of Angular applications but you need to know to pass the data
into the components to configure them.
Angular applications must have a root
component that contains all other components.
Components are created using @Component decorator that is part of @angular/core module.
You can create your own project using
Angular CLI, this command allows you to quickly create an Angular application like
- generate components, services, pipes, directive, classes, and modules, and so
on as per your requirements.
Create your own component (login)
using below command line –
ng g component login
After executing the above Angular CLI
command in your project directory, the result looks like –
D:\Angular\DemoApp>ng g component login
create src/app/login/login.component.html (24 bytes)
create src/app/login/login.component.spec.ts (621 bytes)
create src/app/login/login.component.ts (265 bytes)
create src/app/login/login.component.css (0 bytes)
update src/app/app.module.ts (394 bytes)
And the application login files are
created by default and it looks like –
1. login.component.html
2. login.component.spec.ts
3. login.component.ts
4. login.component.css
5. app.module.ts
And Angular CLI commands also import
the Login component in the Angular module.
See the example in details -
login.component.ts
-
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-login',
templateUrl: './login.component.html',
styleUrls: ['./login.component.css']
})
export class LoginComponent implements OnInit {
constructor() { }
ngOnInit() {
}
}
The above component class shows some
of the most useful @Component
configuration options –
1. Selector
2. TemplateUrl
3. StyleURLs
The selector
– It is a CSS selector that tells Angular to create an instance of this
component wherever it finds the corresponding tag in template HTML. For
example, it is - <app-login></app-login>
The templateUrl
– It is the module-relative address of this component's HTML template
and you can also provide the inline HTML template.
The styleUrls
- It can be used for CSS rules and it will affect the style of the
template elements and you can also provide the inline style CSS.
The components provide you some additional
metadata configurations–
@Component({
changeDetection?: ChangeDetectionStrategy
viewProviders?: Provider[]
moduleId?: string
templateUrl?: string
template?: string
styleUrls?: string[]
styles?: string[]
animations?: any[]
encapsulation?: ViewEncapsulation
interpolation?: [string, string]
entryComponents?: Array<Type<any> | any[]>
preserveWhitespaces?: boolean
// inherited from core/Directive
selector?: string
inputs?: string[]
outputs?: string[]
host?: {...}
providers?: Provider[]
exportAs?: string
queries?: {...}
})
app.module.ts –
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';
import { LoginComponent } from './login/login.component';
@NgModule({
declarations: [
AppComponent,
LoginComponent
],
imports: [
BrowserModule
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }
login.component.html –
<p>
Welcome you, Anil!
</p>
login.component.spec.ts
–
import { TestBed, async } from '@angular/core/testing';
import { AppComponent } from './app.component';
describe('AppComponent', () => {
beforeEach(async(() => {
TestBed.configureTestingModule({
declarations: [
AppComponent
],
}).compileComponents();
}));
it('should create the app', async(() => {
const fixture = TestBed.createComponent(AppComponent);
const app = fixture.debugElement.componentInstance;
expect(app).toBeTruthy();
}));
it(`should have as title 'app'`, async(() => {
const fixture = TestBed.createComponent(AppComponent);
const app = fixture.debugElement.componentInstance;
expect(app.title).toEqual('app');
}));
it('should render title in a h1 tag', async(() => {
const fixture = TestBed.createComponent(AppComponent);
fixture.detectChanges();
const compiled = fixture.debugElement.nativeElement;
expect(compiled.querySelector('h1').textContent).toContain('Welcome to app!');
}));
});
The detail
about Component’s Metadata Properties List -
1.
Selector Property –
The CSS selector that identifies this component in a template.
2.
StyleUrls Property –
The list of URLs to style sheets to be applied to this component's view.
3.
Styles Property – To
be applied the inline styles for the component's view.
4.
Template Property –
To be applied the inline template for the component's view.
5.
TemplateUrl Property
– Used the URLs to an external file containing a template for the view
6.
Animations Property
– Applied the list of animations of this component.
7.
ChangeDetection
Property – The change detection strategy used by this component.
8.
Encapsulation
Property - The style encapsulation strategy used by this component.
9.
EntryComponents
Property – Used the list of components that are dynamically inserted into the
view of this component.
10. ExportAs
Property – The name under which component instance is exported in a template.
11. Host
Property – Used to map the class property to host element bindings for events,
properties, and attributes.
12. Inputs
Property – The list of class property names to data-bind as component inputs.
13. Interpolation
Property – The custom interpolation markers used in this component's template.
14. ModuleId
Property – This is the CommonJS module id of the file in which this component
is defined.
15. Outputs
Property – The list of class property names that expose output events that
others can subscribe too.
16. Providers
Property – The list of providers available to this component and its children.
17. Queries
Property – To configure queries that can be injected into the components.
18. ViewProviders
Property – The list of providers available to this component and its view
children.
Summary -
Components are fundamental building
blocks of UI in Angular applications and it communicates with other components
and services to bring functionality to your applications.
1. It
is a core component of Angular applications.
2. An
angular application must have a root component that contains all other
components.
3. They
have well-defined selector.
4. They
have well-defined styles and styleUrls.
5. They
have well-defined template and templateUrl.
6. They
have well-defined inputs and outputs.
7. They
have well-defined encapsulation and animations.
8. They
have a well-defined lifecycle.
9. They
are self-describing property.
10. And
many more...
Stayed Informed - What Is an EntryComponent in Angular?
Stayed Informed - Why does Angular need entryComponents?
I hope you enjoyed this post. So please write your thoughts in the below comment box. Thank you so much for reading this post.
Stayed Informed - Why does Angular need entryComponents?
I hope you enjoyed this post. So please write your thoughts in the below comment box. Thank you so much for reading this post.