Angular Interview Questions and Answers
Related differences
| Angular vs React | AngularJS vs NodeJS | AngularJS vs Angular |
| Component | Directive |
|---|---|
| To register a component we use @Component meta-data annotation | To register directives we use @Directive meta-data annotation |
| Components are typically used to create UI widgets | Directive is used to add behavior to an existing DOM element |
| Component is used to break up the application into smaller components | Directive is use to design re-usable components |
| Only one component can be present per DOM element | Many directives can be used per DOM element |
| @View decorator or templateurl/template are mandatory | Directive doesn't use View |
Ques 12. What is a template?
A template is a HTML view where you can display data by binding controls to properties of an Angular component. You can store your component's template in one of two places. You can define it inline using the template property, or you can define the template in a separate HTML file and link to it in the component metadata using the @Component decorator's templateUrl property.
Using inline template with template syntax,
import { Component } from '@angular/core';
@Component ({ selector: 'my-app',
template: ' <div>
<h1>{{title}}</h1>
<div>Learn Angular</div>
</div> '
})
export class AppComponent {
title: string = 'Hello World';
}
Using separate template file such as app.component.html
import { Component } from '@angular/core';
@Component ({
selector: 'my-app',
templateUrl: 'app/app.component.html'
})
export class AppComponent {
title: string = 'Hello World';
}
Ques 13. What is a module?
Modules are logical boundaries in your application and the application is divided into separate modules to separate the functionality of your application. Lets take an example of app.module.ts root module declared with @NgModule decorator as below:
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
@NgModule ({
imports: [ BrowserModule ],
declarations: [ AppComponent ],
bootstrap: [ AppComponent ],
providers: []
})
export class AppModule {}
The NgModule decorator has five important(among all) options
- The imports option is used to import other dependent modules. The BrowserModule is required by default for any web based angular application
- The declarations option is used to define components in the respective module
- The bootstrap option tells Angular which Component to bootstrap in the application
- The providers option is used to configure set of injectable objects that are available in the injector of this module.
- The entryComponents option is a set of components dynamically loaded into the view.
Ques 14. What are lifecycle hooks available in Angular? What is the lifecycle of Angular?
Angular application goes through an entire set of processes or has a lifecycle right from its initiation to the end of the application. The representation of lifecycle in pictorial representation as follows:
The description of each lifecycle method is as below,
- ngOnChanges: When the value of a data bound property changes, then this method is called.
- ngOnInit: This is called whenever the initialization of the directive/component after Angular first displays the data-bound properties happens.
- ngDoCheck: This is for the detection and to act on changes that Angular can't or won't detect on its own.
- ngAfterContentInit: This is called in response after Angular projects external content into the component's view.
- ngAfterContentChecked: This is called in response after Angular checks the content projected into the component.
- ngAfterViewInit: This is called in response after Angular initializes the component's views and child views.
- ngAfterViewChecked: This is called in response after Angular checks the component's views and child views.
- ngOnDestroy: This is the cleanup phase just before Angular destroys the directive/component.
Ques 15. What is a data binding?
Data binding is a core concept in Angular and allows to define communication between a component and the DOM, making it very easy to define interactive applications without worrying about pushing and pulling data. There are four forms of data binding(divided as 3 categories) which differ in the way the data is flowing.
From the Component to the DOM:
Interpolation: {{ value }}: Adds the value of a property from the component
<li>Name: {{ user.name }}</li><li>Address: {{ user.address }}</li>Property binding: [property]=”value”: The value is passed from the component to the specified property or simple HTML attribute
<input type="email" [value]="user.email">From the DOM to the Component: Event binding: (event)=”function”: When a specific DOM event happens (eg.: click, change, keyup), call the specified method in the component
<button (click)="logout()"></button>Two-way binding: Two-way data binding: [(ngModel)]=”value”: Two-way data binding allows to have the data flow both ways. For example, in the below code snippet, both the email DOM input and component email property are in sync
<input type="email" [(ngModel)]="user.email">
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