Lesson 9 of 9By Chinmayee Deshpande
Last updated on Dec 15, 20201838Angular is a robust front-end JavaScript framework that is widely used for app development. With the increased popularity, there is a high demand for Angular developers. This article on Angular Interview Questions will present some commonly asked questions and how to answer them. The questions are bifurcated into two levels, beginner and advanced.
To brush up your basics, check out our videos on YouTube. You could also refer to our articles for better clarity. Now, without further ado, let's begin.
Angular was introduced to create Single Page applications. This framework brings structure and consistency to web applications and provides excellent scalability and maintainability.
Angular is an open-source, JavaScript framework wholly written in TypeScript. It uses HTML's syntax to express your application's components clearly.
TypeScript is a superset of JavaScript that offers excellent consistency. It is highly recommended, as it provides some syntactic sugar and makes the code base more comfortable to understand and maintain. Ultimately, TypeScript code compiles down to JavaScript that can run efficiently in any environment.
Data binding is a phenomenon that allows any internet user to manipulate Web page elements using a Web browser. It uses dynamic HTML and does not require complex scripting or programming. We use data binding in web pages that contain interactive components such as forms, calculators, tutorials, and games. Incremental display of a webpage makes data binding convenient when pages have an enormous amount of data.
Angular uses the two-way binding. Any changes made to the user interface are reflected in the corresponding model state. Conversely, any changes in the model state are reflected in the UI state. This allows the framework to connect the DOM to the Model data via the controller. However, this approach affects performance since every change in the DOM has to be tracked.
Single-page applications are web applications that load once with new features just being mere additions to the user interface. It does not load new HTML pages to display the new page's content, instead generated dynamically. This is made possible through JavaScript's ability to manipulate the DOM elements on the existing page itself. A SPA approach is faster, thus providing a seamless user experience.
The following table depicts the aspects of Angular vs AngularJS in detail:
Feature |
AngularJS |
Angular |
Language |
JavaScript |
TypeScript |
Architecture |
Supports Model-View-Controller design |
Uses components and directives |
Mobile support |
Not supported by mobile browsers |
Supports all popular mobile browsers |
Dependency Injection |
Doesn’t support |
Supports |
Routing |
@routeProvider is used to provide routing information |
@Route configuration is used to define routing information |
Management |
Difficult to manage with an increase in source code size |
Better structured, easy to create and manage bigger applications |
Decorators are a design pattern or functions that define how Angular features work. They are used to make prior modifications to a class, service, or filter. Angular supports four types of decorators, they are:
Some of the common advantages of Angular are -
ng new --strict
NGCC Feature - Addition of NGCC features with a program based entry point finder.
Angular Templates are written with HTML that contains Angular-specific elements and attributes. In combination with the model and controller's information, these templates are further rendered to provide a dynamic view to the user.
Annotations in Angular are used for creating an annotation array. They are the metadata set on the class that is used to reflect the Metadata library.
Directives are attributes that allow the user to write new HTML syntax specific to their applications. They execute whenever the Angular compiler finds them in the DOM. Angular supports three types of directives.
The Ahead-of-time (AOT) compiler converts the Angular HTML and TypeScript code into JavaScript code during the build phase, i.e., before the browser downloads and runs the code.
Some of its advantages are as follows.
Components are the basic building blocks of the user interface in an Angular application. Every component is associated with a template and is a subset of directives. An Angular application typically consists of a root component, which is the AppComponent, that then branches out into other components creating a hierarchy.
Pipes are simple functions designed to accept an input value, process, and return as an output, a transformed value in a more technical understanding. Angular supports several built-in pipes. However, you can also create custom pipes that cater to your needs.
Some key features include:
As the name suggests, the interface receives an input value and transforms it into the desired format with a transform() method. It is typically used to implement custom pipes.
import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
name: 'demopipe'
})
export class DemopipePipe implements PipeTransform {
transform(value: unknown, ...args: unknown[]): unknown {
return null;
}
}
These pipes are pipes that use pure functions. As a result of this, a pure pipe doesn't use any internal state, and the output remains the same as long as the parameters passed stay the same. Angular calls the pipe only when it detects a change in the parameters being passed. A single instance of the pure pipe is used throughout all components.
For every change detection cycle in Angular, an impure pipe is called regardless of the change in the input fields. Multiple pipe instances are created for these pipes. Inputs passed to these pipes can be mutable.
By default, all pipes are pure. However, you can specify impure pipes using the pure property, as shown below.
@Pipe({
name: 'demopipe',
pure : true/false
})
export class DemopipePipe implements PipeTransform {
NgModules are containers that reserve a block of code to an application domain or a workflow. @NgModule takes a metadata object that generally describes the way to compile the template of a component and to generate an injector at runtime. In addition, it identifies the module's components, directives, and pipes, making some of them public, through the export property so that external components can use them.
Filters are used to format an expression and present it to the user. They can be used in view templates, controllers, or services. Some inbuilt filters are as follows.
View encapsulation defines whether the template and styles defined within the component can affect the whole application or vice versa. Angular provides three encapsulation strategies:
AngularJS controllers control the data of AngularJS applications. They are regular JavaScript Objects. The ng-controller directive defines the application controller.
The scope in Angular binds the HTML, i.e., the view, and the JavaScript, i.e., the controller. It as expected is an object with the available methods and properties. The scope is available for both the view and the controller. When you make a controller in Angular, you pass the $scope object as an argument.
In Angular, every component has a lifecycle. Angular creates and renders these components and also destroys them before removing them from the DOM. This is achieved with the help of lifecycle hooks. Here's the list of them -
String Interpolation is a one-way data-binding technique that outputs the data from TypeScript code to HTML view. It is denoted using double curly braces. This template expression helps display the data from the component to the view.
{{ data }}
Template statements are properties or methods used in HTML for responding to user events. With these template statements, the application that you create or are working on, can have the capability to engage users through actions such as submitting forms and displaying dynamic content.
For example,
<button (click)="deleteHero()">Delete hero</button>
The template here is deleteHero. The method is called when the user clicks on the button.
Ahead of Time (AOT) compilation converts your code during the build time before the browser downloads and runs that code. This ensures faster rendering to the browser. To specify AOT compilation, include the --aot option with the ng build or ng serve command.
The Just-in-Time (JIT) compilation process is a way of compiling computer code to machine code during execution or run time. It is also known as dynamic compilation. JIT compilation is the default when you run the ng build or ng serve CLI commands.
TypeScript class is one that is used to create components. This genre of class is then decorated with the "@Component" decorator. The decorato’s purpose is to accept a metadata object that provides relevant information about the component.
The image above shows an App component - a pure TypeScript class decorated with the “@Component” decorator. The metadata object that gets accepted by the decorator provides properties like templateUrl, selector, and others, where the templateUrL property points to an HTML file defining what you see on the application.
Angular Services perform tasks that are used by multiple components. These tasks could be data and image fetching, network connections, and database management among others. They perform all the operational tasks for the components and avoid rewriting of code. A service can be written once and injected into all the components that use that service.
While both the concepts deal with Asynchronous events in Angular, Promises handle one such event at a time while observables handle a sequence of events over some time.
Promises - They emit a single value at a time. They execute immediately after creation and are not cancellable. They are Push errors to the child promises.
Observables - They are only executed when subscribed to them using the subscribe() method. They emit multiple values over a period of time. They help perform operations like forEach, filter, and retry, among others. They deliver errors to the subscribers. When the unsubscribe() method is called, the listener stops receiving further values.
ngOnInit is a lifecycle hook and a callback method that is run by Angular to indicate that a component has been created. It takes no parameters and returns a void type.
export class MyComponent implements OnInit {
constructor() { }
ngOnInit(): void {
//....
}
}
The ngFor directive is used to build lists and tables in the HTML templates. In simple terms, this directive is used to iterate over an array or an object and create a template for each element.
<ul>
<li *ngFor = "let items in itemlist"> {{ item }} </li>
</ul>
Template-driven approach
Reactive Form Approach
Bootstrap is a powerful toolkit. It is a collection of HTML, CSS, and JavaScript tools for creating and building responsive web pages and web applications.
There are two ways to embed the bootstrap library into your application.
npm install bootstrap
npm install jquery
Eager loading is the default module-loading strategy. Feature modules under Eager loading are loaded before the application starts. This is typically used for small size applications.
Lazy loading dynamically loads the feature modules when there's a demand. This makes the application faster. It is used for bigger applications where all the modules are not required at the start of the application.
DOM (Document Object Model) treats an XML or HTML document as a tree structure in which each node is an object representing a part of the document.
Angular uses the regular DOM. This updates the entire tree structure of HTML tags until it reaches the data to be updated. However, to ensure that the speed and performance are not affected, Angular implements Change Detection.
With this, you have reached the end of the article. We highly recommend brushing up on the core concepts for an interview. It’s always an added advantage to write the code in places necessary.
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We hope that this article on Angular Interview Questions helped you understand the type of questions asked and how to answer them. But, if you wish to learn Angular and perhaps make a career out of it, certification will come in handy.
Simplilearn's Angular Certification Training Course helps you master front-end web development with Angular. You will learn the knack of creating applications with the help of concepts like facilitating the development of single-page web applications, components, typescript, dependency injection, and directives with this course. The course also includes a real-time project to test your skills.
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Chinmayee is a Research Analyst and a passionate writer. Being a technology enthusiast, her thorough knowledge about the subject helps her develop structured content and deliver accordingly.
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