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Interview Questions

Angular 4 Interview Questions and Answers

Angular 4 Interview Questions and Answers

Angular 4 Interview Questions and Answers

Angular 4 Interview Questions and Answers for beginners and experts. List of frequently asked AngularJS Questions with answers by Besant Technologies. We hope these Angular 4 interview questions and answers are useful and will help you to get the best job in the networking industry. These Angular 4 interview questions and answers are prepared by Angular 4 Professionals based on MNC Company’s expectations. Stay tuned we will update New AngularJS Interview questions with Answers Frequently. If you want to learn Practical Angular 4 Training then please go through this Angular 4 Training in Chennai.

Besant Technologies supports the students by providing AngularJS interview questions and answers for the job placements and job purposes. Angular 4 is the leading important course in the present situation because more job openings and the high salary pay for this Angular 4 and more related jobs.

Best Angular 4 Interview Questions and Answers

Here is the list of most frequently asked Angular 4 Interview Questions and Answers in technical interviews. These Angular 4 questions and answers are suitable for both freshers and experienced professionals at any level. The Angular 4 questions are for intermediate to somewhat advanced Angular 4 professionals, but even if you are just a beginner or fresher you should be able to understand the Angular 4 answers and explanations here we give.

In this post, you will get the most important and top Angular 4 Interview Questions and Answers, which will be very helpful and useful to those who are preparing for jobs.

Angular 4 is the open-source JavaScript framework and mainly used for front-end web applications and it’s completely used for Single Page Applications. Angular 4 training in Chennai by Besant Technologies is the best training Institute and having more than 15+ branches. Besant Technologies has the most experienced trainers and IT professional tutors who are having work experience as the developer, designers, and debuggers. Our trainers have prepared this top and best Angular 4 interview questions and answers.

These Angular 4 interview questions and answers are mainly and completely prepared with complete analysis and these questions are very much important and also these are the questions that were asked in the interview in top MNC companies.

Q1) What are the lead components of Angular?

Answer: Angular contains the below components –

  • Modules
  • Component
  • Services
  • Templates
  • Metadata
Q2) What is CLI and how to use for angular?

Angular CLI is acronym for Command Line Interface and used to build angular apps using in the form of nodejs style modules like you need to install using npm command.

Q3) Difference between constructor and ngOnInit?

Constructor works as default method in TypeScript classes which is used for the initialization.

ngOnInit method is specific to Angular, It is used to define bindingls in Angular.

export class AppTest implements OnInit{


//called intially before the ngOnInit()



//This called after the constructor and after the first ngOnChanges()



Q4) How DI(dependency injection) works in Angular?

Dependency injection (DI), is a design pattern which makes code to write loosely coupled. Angular has its own DI framework for resolving dependencies.

So application will have service which will work based on other service through using DI which makes code loosely coupled which help to reduce dependencies.

Q5) What is ngFor directive?

ngFor directive in Angular used to display each item of the list in the template. Below is the snippet for the same.

*ngFor=”item of obj”>

{{ item }}

Q6) Difference between pure and impure pipe?

Whenever Angular detects changes in the value/parameters which passed to pipe , pure pipe will get called. Whereas impure pipe get called for every change on detection , it does not matter whether the value/parameters changes. i.e On Every keystroke/ mouse-move impure pipe often get called.

Q7) What is RxJS and use of this?

RxJS is a library and used to composing asynchronous and callback-based code in a functional,HttpClient consume and produce RxJS Observables.

Below is the snippet for the same.

import { catchError, retry } from ‘rxjs/operators’;

import { Observable, throwError } from ‘rxjs’;

Q8) What is Angular Router and use of this?

Angular router use to navigate from one to another or next view based on application perform tasks. This model works as brower’s application navigation.

Q9) What is the use of base href tag?

This tag required to routing application which should add element in index.html as the first child to indicate to compose other url of application. Below is the snippet to set the href value as below

<base href=”/”>

Q10) What are the router imports?

Angular Router represents a particular component view for a given URL which is not part of Angular Core. This is available in @angular/router library to import required router components. Below is the snippet for the same.

import { RouterModule, Routes } from ‘@angular/router’;

Q11) List out the router events?

On each navigation, Router emits navigate through the router. Below events is to track the life cycle of the route.

  • ResolveStart
  • ResolveEnd
  • ActivationEnd
  • RouteConfigLoadEnd
  • RoutesRecognized
  • GuardsCheckStart
  • ChildActivationEnd
  • NavigationEnd
  • NavigationCancel
  • NavigationError
  • Scroll
  • NavigationStart
  • RouteConfigLoadStart
  • ChildActivationStart
  • ActivationStart
  • GuardsCheckEnd
Q12) What is Angular Universal?

This is server-side rendering module which recently integrated with Angular CLI. This is available under @angular/platform-server package.

Q13) What are types of compilation in Angular?

Angular has two types to compile your application,

  • JIT – Just-in-Time
  • AOT – Ahead-of-Time
Q14) What is AOT in angular?

AOT – Ahead-of-Time (AOT) is one of the type of compilation that compiles angular app while building time.

Below is the ng build or ng serve command

ng build –aot

ng serve –aot

Q15) What is the syntax of decorator in Angular?

Below is the basic syntax of decorator –

@() with optional parameters

Q16) What is the purpose of common module?

Common module contains services , pipes , HttpClientModule , and directive which provided by @angular/common module. HTTP The commonly-needed services, pipes.

Q17) What is State function?

This function used to define different different states to call on each transition. It takes two arguments unique name and style().

Below is the example for the same.

state(‘closed’, style({

height: ‘600px’,

opacity: 0.9,

backgroundColor: ‘green’


Q18) Which are the class decorators in Angular?

Class decorator appears before a class definition. Below is the following list of decorators which comes under class decorators.






Q19) What are the class field decorators?

This statements declared immediately before all the field which has define in the class. Below is the example for the same.

@Input() myPriority;

@Output() event1 = new EventEmitter();

Q20) What is One-way binding in AngularJS?

One way binding is used for one-time expression and represents as double colon – “::”.

Q21) What is the (ngModel) used for in AngularJS?

This used for Two-way data binding

Q22) What is a digest cycle in Angular?

Digest cycle is the code that runs at an interval which can be set or simply works fast as default.

Q23) What Is @ngmodule in angular?

It’s a Angular 2 module. It’s a decorator function which allows users to mark something like module/component and it enables additional data.

Q24) What Is @inputs In Angular?

It comes under Angular 2 which allows to pass data into controller and template through html and custom properties. This allows to reuse components and display the same for each instance on the rendering.

Q25) How Lifecycle hooks works in order?





Q26) When ngOnInit used to call in Angular?

In Angular, After display first bound properties nogOnInit will get called.

Q27) How async pipe prevent memory leeks?

Whenever any component gets destroyed/unmounted , async pipe works automatically to avoid memory leaks.

Q28) What is lean component mean in Angular?

The lean component used only to display the data.

Q29) Why do we required route guards in Angular?

This is one of the interface which tell the router to allow or not the navigation on requested route.

Q30) What is the use of RouterOutlet?

RouterOutlet required to bind the components whenever the navigation get called.

Q31) What are the building blocks of Angular application?

Angular application is made by using the below.

  • Blocks
  • Component
  • Services
  • Orders
  • Template
  • DataNemo
  • Pro injection
  • Lane
Q32) What is mean of reliability injection in angular?

Whenever there is dependencies on the component like one component depends on another, this particular function is turned on and off when the functionality is turned on.

Q33) What is the Difference between ng-class and ng-style?

The CSS class loading is possible in ng-class , Whereas we can set the CSS style in ng-style we can set the CSS style.

Q34) what is binding and describe the types?

This is a process to get the data combine which always used to work for each flow. We have two types for this-

  • Data binding
  • Event binding
Q35) What are the different ng commands in angular?
  • Ng new
  • Ng generate
  • Ng build
  • Ng serve
  • Ng test
Q36) What are the data types define in TypeScript?
  • String
  • Any
  • Void
  • Boolean
  • Number
Q37) What is required to validate the form inputs?

Form inputs used to validate with cNg-Validate and such inputs like barcodes, mobile numbers, email.

Q38) What are the ways to create custom directive in angular?
  • Element directive
  • CSS directive
  • Attribute directive
Q39) Describe about the Directive and Directive Types?

Directive used to make DOM level changes which works dynamically.

  • Attribute Directive
  • Component Directive
  • Structural Directive
Q40) What is data Binding in angular and how it works?

Data binding used to communicate between template and component and it worked whenever change event will occur. It has two types, below are the types.

  • One-way
  • Two-way
Q41) What is Singleton pattern and how it works in AngularJS?

This design pattern restrict to create a object again and will pass the same object which is available. In AngularJs dependency injection used to enable this pattern , once this is enabled then class create object.

Q42) What are the event listener directives that attach to HTML element?


Q43) What are the various styling form in Angular which has to adds in CSS classes by ngModel?

ngModel adds below CSS classes to allow styling and control.

  • ng-pristine
  • ng-dirty
  • ng- valid
  • ng- invalid
Q44) What are the built-in validators in AngularJS list out few of them?

Below is the few validators which are built-in .

  • min
  • max
  • required
  • type=”number” OR type=”email”
Q45) What are the Structural and Attribute directives Structural in Angular JS?

To Add or Remove Items from DOM below are the one


Below are the attributes which appears changes on element


Q46) what angular.json file represent in Angular CLI?

Angular CLI works to generate workspace directory in AngularJS.

Q47) How to use *ngFor Loop directive?

This works on collection of data and NgFor is a directive that iterates on collection object.

Q48) What type of data work with an async pipe , list out few?
  • Observable
  • Promise
Q49) Difference between scan() vs reduce() in AngularJS?

Scan – This applied with function for each item emitted which is perform by Observable, sequentially, and emit on each success value.

Reduce – This works same as Scan except it emit only final value.

Q50) How the TypeScript code is converted into JavaScript code, brief the process?

This is known as Transpiling. TypeScript code used to write in Angular application but internally it gets transpiled into equivalent JavaScript.

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