Angular interview questions and answers-2020

Latest Angular interview questions and answers- 2020

1. What is Angular framework?

Angular is a TypeScript-based open-source front-end development platform that makes it easy to build the applications like web/mobile/desktop. The major features of this framework such as Single page application, Component, Directives, Dependency injection, end to end tooling, and many more other features are used to ease the development.

2. What is TypeScript?


TypeScript is a typed superset of JavaScript with extra features like classes, async/await, and many other features, and compiles to plain JavaScript. Angular built entirely in TypeScript and used as a primary language. You can install it globally as
   
         npm install -g typescript

 Let's see a simple example of TypeScript usage,

 
function greeter(person: string) {
return "Hello, " + person; }
let user = "Sontosh";
document.body.innerHTML = greeter(user);
The greeter method allows only string type as an argument.

3. What is the difference between AngularJS and Angular?

Angular is a completely revived component-based framework in which an application is a tree of individual components.
Some of the major difference in tabular form
                          Angular JS
                                  Angular
It is MVC based architecture
It is based on Services/Controller
It uses  JavaScript to build the application
It uses Typescript to build the application
Based on controllers concept
It is  based  on the component UI approach
It only uses on Desktop Applications
It  uses both mobile & desktop applications
Difficulty in SEO friendly application development
Ease to create SEO friendly applications

4. What are the key components of Angular?

Angular has the below key components,
  1. Component: These are the basic building blocks of angular application to control HTML views.
  2. Modules: An angular module is a set of angular basic building blocks like component, directives, services, etc. An application is divided into logical pieces and each piece of code is called "module" which performs a single task.
  3. Templates: This represents the views of an Angular application.
  4. Services: It is used to create components that can be shared across the entire application.
  5. Metadata: This can be used to add more data to an Angular class.

5. What are directives?

Directives add behavior to an existing DOM element or an existing component instance.

import { Directive, ElementRef, Input } from '@angular/core';

 @Directive({ selector: '[myHighlight]' })
export class HighlightDirective {
    constructor(el: ElementRef) {
       el.nativeElement.style.backgroundColor = 'yellow';
    }
}
Now this directive extends HTML element behavior with a yellow background as below

 <p myHighlight>Highlight me!</p>
<p myHighlight>Highlight me!</p>

6. What are the components?

Components are the most basic UI building block of an Angular app which formed a tree of Angular components. These components are a subset of directives. Unlike directives, components always have a template and only one component can be instantiated per an element in a template. Let's see a simple example of an Angular component

import { Component } from '@angular/core';

 @Component ({
   selector: 'my-app',
   template: ` <div>
      <h1>{{title}}</h1>
      <div>Learn Angular6 with examples</div>
   </div> `,
})

 export class AppComponent {
   title: string = 'Welcome to Angular world';
}

7. What are the differences between Component and Directive?

In a short note, A component(@component) is a directive-with-a-template.
Some of the major differences are mentioned in a tabular form
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
Directives is used to add behavior to an existing DOM element
Components is used to break up the application into smaller components
Directives is used 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 template URL/template is mandatory
Directive doesn’t  use View


 8.  What is a template?


A template is an HTML view where you can display data by binding controls to the 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';



}

9.  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 ]



})



export class AppModule { } 

The NgModule decorator has three 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

10.  What are lifecycle hooks available?



The angular application goes through an entire set of processes or has a lifecycle right from its initiation to the end of the application.


The description of each lifecycle method is as below,

ngOnChanges: When the value of 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.

11.  What is a data binding?



Data binding is a core concept in Angular and allows us 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.


i.  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>

ii. 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">

 iii. 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>


iv. 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">



12. What is Angular CLI?



Angular CLI(Command Line Interface) is a command-line interface to scaffold and build angular apps using nodejs style (commonJs) modules. You need to install using below npm command,

npm install @angular/cli@latest
Below are the list of few commands, which will come handy while creating angular projects
i. Creating New Project: ng new

ii. Generating Components, Directives & Services: ng generate/g The different types of commands would be,
ng generate class my-new-class: add a class to your application
ng generate component my-new-component: add a component to your application
ng generate directive my-new-directive: add a directive to your application
ng generate enum my-new-enum: add an enum to your application
ng generate module my-new-module: add a module to your application
ng generate pipe my-new-pipe: add a pipe to your application
ng generate service my-new-service: add a service to your application
iii. Running the Project: ng serve