Angular 7 ngIf Directive

Use of *ngIf directive to change the output conditionally:

Example:

component.ts file:

import { Component, OnInit } from '@angular/core';  
 
@Component({  
  selector: 'app-server2',  
  templateUrl: './server2.component.html',  
  styleUrls: ['./server2.component.css']  
})  
export class Server2Component implements OnInit {  
 allowNewServer = false;  
 serverCreationStatus = 'Server not created.';  
  serverName = 'TestServer';  
  serverCreated = false;  
 
  /*constructor() {  
    setTimeout(() =>{  
      this.allowNewServer = true;  
    }, 5000);  
  }*/  
 
  ngOnInit() {  
  }  
  onCreateServer() {  
    this.serverCreated = true;  
    this.serverCreationStatus = 'Server created with the Name: ' + this.serverName;  
  }  
  OnUpdateServerName(event: Event) {  
    this.serverName = (<HTMLInputElement>event.target).value;  
  }  
}

component.html file:

<p>  
  Server2 is working fine.  
</p>  
 
<label>Name of the Server: </label>  
<!--<input type="text"  
       class="form-control"  
       (input)="OnUpdateServerName($event)">-->  
<input type="text"  
       class="form-control"  
[(ngModel)]="serverName">  
<!--<p>{{serverName}}</p>-->  
<button  
  class="btn btn-primary"  
  [disabled]="allowNewServer"  
  (click)="onCreateServer()">Add</button>  
<p *ngIf="serverCreated">Server created with the Name: {{serverName}}</p>

Output:

Now, change the input value and click on the “Add Server” button.

Output:

Explanation:

In the above example, we are using the *ngIf directive to change the condition to display the output accordingly.

The view-source of the output can be checked before and after adding the server to know exactly how a structural directive can change the DOM.

Before adding the server:

After adding the server:

*ngIf directive with an Else condition:

An Else condition can be used with *ngIf directive to display the output if *ngIf is not true.

Example:

//component.html file:

<p>
 Server2 is working fine.
</p>
 
<label>Name of the Server: </label>
<!--<input type="text"
      class="form-control"
      (input)="OnUpdateServerName($event)">-->
<input type="text"
      class="form-control"
      [(ngModel)]="serverName">
<!--<p>{{serverName}}</p>-->
<button
 class="btn btn-primary"
 [disabled]="allowNewServer"
 (click)="onCreateServer()">Add</button>
<p *ngIf="serverCreated; else noServer">Server created with the Name:  {{serverName}}</p>
<ng-template #noServer>
 <p>No Server is created.</p>
</ng-template>

Output:

Now click on the “Add Server” button.

Output:

The reverse case can be checked by using the negation (!) sign.

Example:

component.html file:

<p>
 Server2 is working fine.
</p>
 
<label>Name of the Server: </label>
<!--<input type="text"
      class="form-control"
      (input)="OnUpdateServerName($event)">-->
<input type="text"
      class="form-control"
      [(ngModel)]="serverName">
<!--<p>{{serverName}}</p>-->
<button
 class="btn btn-primary"
 [disabled]="allowNewServer"
 (click)="onCreateServer()">Add</button>
<p *ngIf="!serverCreated; else noServer">Server created with the Name:  {{serverName}}</p>
<ng-template #noServer>
 <p>No Server is created.</p>
</ng-template>

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