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Angular Learning

rohithv07 profile image Rohith V ・2 min read

On my journey, today I learned about the directives.

What is a directive

It can be defined as an instructions which tells to change the DOM. It can be for :

  • Component : Directives with a template

  • Structure : Change the structure of the elements.

  • Attribute : Change the appearence or behavior of elements.

A sample example code :

<p appTurnGreen>Background will turn to green</p>


Inside the component.ts file
@Directive({
      selector: '[appTurnGreen]'
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Inbuilt Directives :

1) ngIf : This directive is used to output the data conditionally.
A code example for ngIf

<label>Server Name</label>
<!-- <input type="text" class="form-control" (input)="onUpdateServerName($event)">  Access to event data -->

<input type="text" class="form-control" [(ngModel)]="serverName"> <!-- Two way binding -->

 <!-- <p>{{ serverName }}</p> -->
<button 
class="btn btn-primary" 
[disabled]="!allowNewServer"
(click)="onCreateServer()"> 

<!-- <p [innerText]="allowNewServer"></p> -->
<!-- <p> {{ serverCreationStatus }}</p> -->

<p *ngIf="serverCreated">Server was created with name {{ serverName }}</p>
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We have to use * in front of the ngIf.

It needs to output the servername after typing a name on the input text and then clicking the button. We also need to configure the component.ts file

export class ServersComponent implements OnInit {
    allowNewServer = false;
    serverName = 'TestServer';
    serverCreated = false;

  constructor() { 
    setTimeout(() => { 
        this.allowNewServer = true;
    },2000);
  }

  ngOnInit(): void {
  }

  onCreateServer() {
    this.serverCreationStatus = this.serverName + ' Server was created';
    this.serverCreated = true;
  }

  onUpdateServerName(event: any) {
    this.serverName = (<HTMLInputElement>event.target).value;
  }

}
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1

  1. ngStyle and ngClass :

ngStyle is used for styling elements dynamically.
ngClass is used to apply CSS classes dynamically.

<p [ngStyle]="{ backgroundColor: getColor() }"
[ngClass]="{ online: serverStatus === 'online'}">Inside the {{'Rohith server'}} component with ID {{ serverId }} and status {{ getServerStatus() }}</p>
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Here we wrap ngClass and ngStyle inside square brackets as we apply property binding.

@Component({
    selector: 'app-server',
    templateUrl: './server.component.html',
    styles: [`
    .online {
        color: white;
    }
    `]
})
export class ServerComponent {
    serverId: number = 10;
    serverStatus: string = 'offline';

    constructor() {
        this.serverStatus = Math.random() > 0.5 ? 'online' : 'offline';
    }

    getServerStatus() {
        return this.serverStatus;
    }

    getColor() {
        return this.serverStatus === 'online' ? 'green' : 'red';
    }
}
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2

  1. ngFor : This is generally used for outputting the list.
<app-server *ngFor="let server of servers"></app-server>
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  • needs to be used infront of ngFor as it is a structural directive.
@Component({
  // selector: 'app-servers', // by element
  // selector: '[app-servers]', // by attribute
  selector: '.app-servers', // by class
  templateUrl: './servers.component.html',
  styleUrls: ['./servers.component.css']
})
export class ServersComponent implements OnInit {
    allowNewServer = false;
    serverCreationStatus = 'No server was created'
    serverName = 'TestServer';
    serverCreated = false;
    servers = ['TestServer', 'TestServer2']

  constructor() { 
    setTimeout(() => { 
        this.allowNewServer = true;
    },2000);
  }

  ngOnInit(): void {
  }

  onCreateServer() {
    this.serverCreationStatus = this.serverName + ' Server was created';
    this.serverCreated = true;
    this.servers.push(this.serverName);
  }

  onUpdateServerName(event: any) {
    this.serverName = (<HTMLInputElement>event.target).value;
  }

}
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3

Github Repo :

Angular Study

Till now I learned about components, data binding, directives and moving forward with doing a sample project.

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