Angular 4 Interview Questions

Angular 4 is a JavaScript framework that is widely used for creating and developing web applications as well as mobile applications in various languages such as JavaScript, HTML, and TypeScript. In other words, it can be said that Angular 4 is a superset of JavaScript. Here are some Angular 4 interview questions which may help the aspirants to get their concept clear. There are numerous features such as animation, Http service, navigation, menus, toolbar, auto-complete and many more. Recruiters go through a lot of processes to hire developers for Angular 4. This article consists of the latest Angular 4 interview questions and answers to get their basics clear.

Most Frequently Asked Angular 4 Interview Questions and Answers

In Angular 4, data binding is a core concept that allows defining communication between the DOM and a component. This makes it easy to define interactive applications without complexion of pulling and pushing data.

In Angular, Dependency Injection (DI), is an application design pattern that is very important. Angular has its own unique DI framework that is usually used in the design of applications developed in angular so that their efficiency and modularity can be increased. The services or objects needed by a class to perform its functions are known as Dependency. The coding pattern in which a class asks for a dependency from external sources instead of creating them itself, that coding pattern is known as dependency injection.

There are several new features added in Angular 4 such as Router ParamMap, TypeScript Compatibility, Animation Package, smaller and quicker, dynamic components, Angular Universal and many more.

Compared to Angular 4, Angular 5 has plenty of feature additions, bug fixes and service improvements implemented to it. The addition of a build optimizer to Angular 5 is a pleasant surprise for developers. Added to CLI, this tool can help developers to create smaller bundles for the application. It also increases the boot speed of the application for users. Few other crucial differences between these two versions will be compiler improvements, the addition of HttpClient and new router lifecycle events. All these features have newly included to the Angular 5.

Lazy loading is used to load only those components that are needed when starting up the application. It can be seen in the app.module.ts when the app is started that all components are imported and all of them are put under the declarations array. Loading all the components when the app starts makes it slow. To enable lazy loading in Angular 4, the following steps are included:

  • The feature model is created and then routing is done
  • Child Route is created
  • Run

In this way, in Angular 4, lazy loading may be enabled easily. One should have to be careful with errors to implement it correctly.

Ng class Ng style
Ng class has the function of translating the given objects into a class attribute. There is a proper syntax for doing the same. In Angular 4, ng style is basically used while interpolating javascript object into a style attribute in place of a CSS class.
While working with ng-class, CSS class defined can be loaded easily just like Bootstrap. Another function of Ng style is to interpolate any variable into a style attribute. But this function does not work before the Internet Explorer 11 version.
Ng class can be used to set the CSS class in a dynamic way for a DOM element. Ng style helps to set the style properties of a given DOM element.

In Angular Roulet-Outer works as a placeholder. Placeholder is used to load the different components dynamically based on the activated component or the current route state. Using the router-outlet directive and the components that are activated navigation can be done, all this will take place inside the router outlet so that its content can be loaded. Router-outlet is used in the HTML template to enable routing.

Components are very important in Angular 4 web applications. Just like bricks are in the building, components are in the web application of angular. To define components in angular @component decorator is used. In a component, there are properties like selector, template, style, etc. Using these properties component specifies the metadata that is required to process the component.

If Else statement in Angular 4 can be written using the following syntax-
Open /src/app/app.components.ts:

Export class AppComponent {
   Title – ‘app works!;
}

Open /src/app/app.component.html
<div *ngIf = “ title; else login”>
The user is logged in. </div>
<ng-template #login> in order to login please continue. </ng-template>
Then statement can be written using following syntax-
<div *ngIf = “title; then logout else login “> </div>
<ng-template #login> please login to continue . </ng-template>
<ng-template #logout> Hi abc, <button> logout now </button> . </ng-template>

The components are the part where the developers spend most of their time while developing an application. The components in Angular 4 are nothing but classes and they are designated as a component with the help of a component decorator. Each component has a template that is defined through which it can communicate with the code of the application that is defined in the component class. Let’s look at how the components are structured.

  • Importing Components
  • The Component Decorator
  • The Component Class
  • Creating a Component:

Creating components becomes a clinch in the Angular CLI.

Command: > ng g component my-new-component>

  • Angular CLI is invoked by ng.
  • Generate is written in short as “g”(Note: Full keyword can also be used instead of g)
  • The type of element that is about to be generated is known as Component
  • And at last, comes the name of the component

These are the following steps that should be followed while installing Angular 4:

  • Firstly make sure that node version 6.9 and npm above 3 are present on the computer.
  • After that by using node check the version
  • Install angular CLI after that using npm install -g @angular/CLI
  • -g will install the angular globally on the system and this command has to be run only once.
  • Angular Project is created using 'ng new angularprojectname'.
  • Angular is updated to angular 4 by running the command below:
    For Windows- npm install @angular/common@next @angular/compiler@next @angular/compiler-cli@next @angular/core@next
    @angular/forms@next @angular/http@next @angular/platform-browser@next @angular/platform-browser-dynamic@next
    @angular/platform-server@next @angular/router@next @angular/animations@next --save
    For Linux/Mac- npm install @angular/{common,compiler,compiler-cli,core,forms,http,platform-browser,platform-browser-
    dynamic,platform-server,router,animations}@next --save
  • Upgrage the typescript version by running the following command: npm install typescript@2.2.1 -- save.
    Ignore the warning that shows up and then check the angular version by ‘ng-v’, you will see that the version will be changed from 2.2.4 to 4.1.0.

import {
Component,
ViewContainerRef,
ViewChild,
ComponentFactoryResolver,
ComponentRef,
ComponentFactory
}

from '@angular/core';
import { MessageComponent } from './message.component';
@Component(
{
selector: 'app-root',
templateUrl: './app.component.html'
}
)
export class AppComponent {
title = 'app';
}

  • Step 1: Installing the node package
  • Step 2: Adding cookies service to app.module.ts as a provider
  • Step 3: Importing as well as injecting the same into a component.

Code involved :
npm install ngx-cookie-service –save
@NgModule({
...,
providers: [ CookieService ]
import { CookieService } from 'ngx-cookie-service';
constructor( private cookieService: CookieService ) { }
ngOnInit(): void {
this.cookieService.set( 'Test', 'Hello World' );
this.cookieValue = this.cookieService.get('Test');
}