Angular 4 if else then conditions

Angular 4 If Else and Then Conditions [7 Best Examples]

The “If” evaluates expression and then renders the “else” or “then” template in its place when expression is “truthy” or “falsy” respectively.

Stayed Informed – Angular 4 vs. Angular 2
Stayed Informed – Angular 2 if else examples

Then: - This template is the inline template of “If” unless bound to a different value.
Else: - This template is blank unless it is bound.

Selectors: -
1.      If
2.      If then
3.      If else

The multiple examples for Angular 4 if else and then as given bellows,

Syntax:-
<element *ngIf="[condition expression]; else [else template]"> </element>

Syntax:-
<div *ngIf="users | async; else loadingGrid; let user">
  <p>{{user.Id}}</p>
  <p>{{user.name}}</p>
  <p>{{user.Age}}</p>
</div>
 
<ng-template #loadingGrid>loading...</ng-template>

Syntax :- We can also use 'then else'
<div *ngIf="isValid;then then_content else other_content">If IsValid then display other</div>

<ng-template #then_content>content here...</ng-template>
<ng-template #other_content>other content here...</ng-template>

Example 1 as,
<div *ngIf="isValid;else other_content">
    <p>Display valid content here ...</p>
</div>

<ng-template #other_content>
     <p>Other content here...</p>
</ng-template>

Example 2 as,
<div *ngIf="title; then logout else login"></div>

<ng-template #login>Please login to continue.</ng-template>
<ng-template #logout>Hi Anil!<button>Logout</button>.</ng-template>

Example 3 as,
//our root app component
import {Component, NgModule} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'

@Component({
  selector: 'else-cmp',
  template: `<button (click)="isValid = !isValid">update</button>
    <div *ngIf="isValid; else other_content">
       content here ...
    </div>
    <ng-template #other_content>other content here...</ng-template>`,
})
export class ElseComponent {
  isValid:boolean = true;
  constructor() {
  }
}
@Component({
  selector: 'else-then-cmp',
  template: `
      <button (click)="isValid = !isValid">update</button>
       <div *ngIf="isValid;then content else other_content"></div>
       <ng-template #content>content here...</ng-template>
       <ng-template #other_content>other content here...</ng-template> 
  `,
})
export class ElseThenComponent {
  isValid:boolean = true;
  constructor() {
  }
}

@Component({
  selector: 'my-app',
  template: `
    <h4>Using else :</h4>
    <else-cmp></else-cmp>
    <h4>Using else then:</h4>
    <else-then-cmp></else-then-cmp>
  `,
})
export class App {
  isValid:boolean = true;
  constructor() {
  }
}

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App , ElseComponent, ElseThenComponent],
  bootstrap: [ App ]
})
export class AppModule {}

Stayed Informed - Best Angular 2 Interview Questions and Answers

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