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Top Angular Interview Questions and Answers

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angular interview question

Angular is one of the most popular JavaScript single-page application frameworks. It is also quite vast and difficult to navigate. Even more difficult is to get answers to the interview questions on Angular as it is very confusing to know which parts of the Angular framework you should familiarize yourself with. Hence, we have come up with a compilation of Angular interview questions and answers that are asked in these interviews most frequently

1. Angular Basic Interview Questions

2. Angular Intermediate Interview Questions

3. Angular Advanced Interview Questions

Most-Asked Angular Interview Questions and Answers

Q1. What is Angular?
Q2. What are the technologies used in Angular?
Q3. Why were client-side frameworks like Angular introduced?
Q4. How does an Angular application work?
Q5. What is TypeScript?
Q6. Write a pictorial diagram of Angular architecture?
Q7. What is metadata?
Q8. What is the difference between constructor and ngOnInit?
Q9. How is Dependency Hierarchy formed?
Q10. What is the purpose of the async pipe?

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Angular Basic Interview Questions

Let’s start with the basic Angular interview questions and answers for freshers.

1. What is Angular?

Angular is an open-source web application development framework created by Google. It is used to build frontend, single-page applications that run on JavaScript. It is a full-fledged framework, i.e., it takes care of many aspects of frontend web applications such as HTTP requests, routing, layout, forms, reactivity, validation, etc.

2. What are the technologies used in Angular?

Angular is a modern frontend JavaScript framework developed by Google. Angular itself makes use of several technologies for several reasons to accomplish certain tasks easily as well as to allow developers to have a better experience while developing applications with it. Angular uses TypeScript, which is a superscript of JavaScript. So, any valid JavaScript is a valid TypeScript. However, TypeScript allows us to write JavaScript as a strongly typed language, and we can define our own types as well, which makes catching bugs much easier. It also uses RxJS, which allows developers to better deal with asynchronous operations.

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3. Why were client-side frameworks like Angular introduced?

Before JavaScript-based client-side frameworks, the way dynamic websites worked was by taking a template that is nothing but HTML code with spaces left empty for feeding data and content into those templates. This data was usually fetched from a database. After combining the template and data, we would serve the generated HTML content back to the user. As you can see, it was a bit complicated, and in some cases, it took a lot of processing.

To overcome these issues, people came up with another approach in which they send the necessary data to render a page from their web servers to the web browsers and let JavaScript combine this data with a predefined template. Since now, even mobile phones are powerful enough to do this kind of processing, the servers can now just send the data to a client over the internet in a recognizable format, i.e., JSON, XML, etc. This drastically reduces the processing done on the servers and improves performance.

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4. How does an Angular application work?

The working of Angular is based on its components. So the working of the Angular application starts with the configuration file ANGULAR.JSON. The builder refers to this file to find the paths, configurations and the main file. Now the process finally starts. Next comes the MAIN.TS file that acts as the entry point for the configuration file. It basically helps in creating the browser environment that enables it to run the application. Now, the bootstrapping of the Angular application is done through the APP.MODULE.TS. Now the app component that gets bootstrapped is stored in the APP.COMPONENT.TS file. Now the INDEX.HTML file is called and is used to ask Angular to load the application component. After the component is loaded, the content gets displayed from the APP.COMPONENT.HTML file. This is how the Angular application works and the components discussed here help to achieve so.

5. What is TypeScript?

The TypeScript feature offered by Angular is preferred by a majority of Front-End Developers. TypeScript helps in efficiently detecting bugs and helps in easy compilation by its automatic populating functionality. Also, it offers rich interfaces, access modifiers, hybrid types etc. All these combined lead to reduction in the developing time.

6. Write a pictorial diagram of Angular architecture?

The architecture of Angular comprises the following elements. The pictorial representation of the same is given below:

  • Components and Templates
  • Ng Modules
  • Metadata
  • Data Binding
  • Directives
  • Services
  • Dependency Injection

pictorial diagram of Angular architecture

7. What is metadata?

Using metadata is how we tell Angular how to process a class. When we use a component, it acts as a class unless we tell Angular that it’s a component, and we do this with the help of metadata. Metadata is attached in TypeScript using a decorator. Decorators are functions that know the configuration of classes and how they are supposed to work.

8. What is the difference between constructor and ngOnInit?

The difference between constructor and ngOnInit is given below:

Basis Constructor ngOnInit
Objective. The objective of a Constructor is to start class members ngOnInit is used in case of startup/announcement and avoids things to work in builders.
Usage A Constructor should be used to set up Dependency Injection, Initialization of class fields, etc. ngOnInit is used to write the work code that  executes as soon as the class is instantiated.

9. How is Dependency Hierarchy formed?

The dependency injection system of Angular is hierarchical. It consists of a tree of injectors that stands parallel to the application’s component tree. The Dependency Hierarchy is formed with the configurations. The reconfiguration of the injectors can be done at any given level of the component tree. The providers for different injectors can also be configured in the injector hierarchy.

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10. What is the purpose of the async pipe?

The purpose of the async pipe is basically to mark the components that need to be checked for changes. It subscribes to an Observable or Promise and returns the latest value it has emitted. Once this new value gets emitted, the components are marked by the async pipe. Now, whenever any component is destroyed, the async pipe detaches or unsubscribes automatically. Similarly, if the expression reference of the component changes, the async pipe detaches or unsubscribes from the old Observable or Promise and subscribes to a new one.

11. What is the option to choose between inline and external template?

Usually, inline templates are used for small codes and external templates are used for comparatively bigger views. However, the choice of inline or external templates is sometimes based on organization policy, situations etc.

12. What is the purpose of ngFor directive?

Whenever it is required to repeat a part or portion of an HTML template once for each item from a collection, the ngFor directive is used. Basically it creates a template for each time as the iteration becomes easier using ngFor directive.

13. What is the purpose of the ngIf directive?

The purpose of the ngIf directive is to remove or recreate a part of DOM tree in alignment to an expression. If the ngIf directive finds that the expression is evaluating to be false, the element is removed from the tree, else a matching element is inserted into the DOM tree.

14. What happens if you use script tag inside template?

If we use script tag inside template, Angular marks the value as unsafe and automatically initiates the process of sanitizing it. This eradicates the script tag but the content is kept safe, i.e. the text element. This entire process results in eliminating the risk of injection attacks.

15. What are template expressions?

A template expression in Angular is an expression that is represented in double curly braces ‘{{ }}’ and produces a value. The template expression is executed by Angular and is assigned to a property of a binding target. Now, the binding target can be any of these- HTML element, a directive or even a component.

16. What are template statements?

The methods or properties in Angular that are used in HTML in response to user events are called template statements. These template statements allow your application to engage users through actions like dynamic content display or form submissions etc.

17. What is the difference between Angular and AngularJS?

Following are some of the major and significant differences between Angular and AngularJS:

Features Angular AngularJS
Architecture It makes use of directives and components It supports the Model-View-Controller or MVC model
Language It uses TypeScript language, a superset of JavaScript that is typed statistically It uses JavaScript, a dynamically typed language
Expression Syntax Angular uses () to bind an event while [] to bind a property It requires professionals to use the correct ng directive to bind a property or an event
Mobile Support Angular offers mobile support Unlike Angular, AngularJS does not offer mobile support
Routing It uses @RouteConfig{(…)} It uses $routeprovider.when()
Dependency Injection It supports hierarchical dependency injection, along with a unidirectional tree-based change direction It does not support dependency injection
Structure Its simplified structure makes it easy for professionals to develop and maintain large applications easily It is comparatively less manageable

18. What are some advantages of using Angular?

Using Angular has several advantages, which are listed below:

  • Angular is built using TypeScript, which allows developers to write strongly typed code that will get transpiled into JavaScript. The benefits of strongly typed code are that it is easy to read, maintainable, and less prone to errors. Also, it provides better tooling with type hints and code completion.
  • Angular allows us to separate our code into modules, which can be used to wrap functionalities related to a specific task such as HTTP communication, data validation, routing, etc.
  • Angular has a large ecosystem of tools, libraries, frameworks, plugins, etc. that make the whole development experience much faster and enjoyable. These tools and libraries include Angular CLI, RxJS, NgRx, etc.

19. How do you categorize data binding types?

To categorize data binding in Angular, it is divided into various types. Data Binding in Angular is categorized into following types:

  • One Way Data Binding
  • Two-Way Data Binding

In One way data binding, the changes in the state affect the view from component to view template. On the contrary it is also possible that the change in the view affects the state by changing it from view template to component.

Now, coming to Two-way Data Binding, the changes in the view can lead to change in the model. Similarly, any changes in the model can change the view from component to view template.

The various types under Two-Way Data Binding are:

  • Interpolation
  • Property binding
  • Class binding
  • Style binding
  • Attribute binding
  • Event binding
  • Two-way binding

20. What is a parameterized pipe?

In Angular, pipes are used to transform the raw data into a required format before the final display to the end-users. These pipes are broadly categorized into 2 categories:

1- Built-in Pipes,

2- Custom Pipes

Built-in Pipes are further divided into 2 types – Parameterized Pipes and Chaining Pipes.

Parameterized Pipes refer to the pipes that carry parameters. We can use these pipes to pass n number of parameters by giving a colon (:) in the command.

21. What are custom elements?

A custom element is used to extend HTML, wherein you can define a tag whose content is created and controlled by JavaScript code.

22. Do I need to bootstrap custom elements?

No, you do not need to bootstrap custom elements as they bootstrap automatically when added to the DOM. Also, the custom elements in Angular get automatically destroyed when removed from the DOM.

23. How do you define typings for custom elements?

Defining typings for custom elements in Angular can be done by using NgElement and WithProperties exported from @angular/elements. The following component is a simple container with input property:

@Component(…)
class MyDialog {
@Input() content: string;
}

24. Explain how custom elements work internally?

Let us understand the internal working of custom elements in steps:

  • Registration of the custom elements: Angular registers the custom elements using the createCustomElement() function. This function converts a component into a class that can be registered with the browser as a custom element.
  • Addition of the custom element to DOM: The custom element is added to DOM similar to a built-in HTML.
  • Browser instantiates component based class: Once the custom element is added to DOM, an instance of the registered class is created by the browser and added to the DOM.
  • Data binding and Change detection: In the final step, the created instance enables data binding and change detection. The template content is rendered using the component and DOM data.

25. How to transfer components to custom elements?

There are two important steps to be followed in order to transfer components to custom elements:

  • Creating a custom element class: As a first step, build a custom element class using the createCustomElement() function provided by Angular. The function converts an Angular component (including its dependencies) to a custom element. The NgElementConstructor interface is implemented through this conversion which, in turn, creates a constructor class that is used for producing a self-bootstrapping instance.
  • Registering element class with browser: The customElements.define() function is used to register the configured constructor, and its associated custom-element tag with the browser’s CustomElementRegistry.

26. What are the mapping rules between Angular component and custom element?

The important mapping rules between Angular component and custom element are given below:

  • The component input properties are parsed with the corresponding attributes for the custom element using the createCustomElement() API.
  • TThe Component outputs are dispatched as HTML Custom Events and have the name of the custom event that also matches the output name.

27. How do you chain pipes?

The syntax used for chaining pipes in Angular is given in the following example:

Today is {{ today | date:’fullDate’ | uppercase}}.


28. What is a custom pipe?

In Angular, you can create custom pipes. They are nothing but customized pipes and were earlier known as ‘Filters’ in Angular. Commonly, custom pipes are defined as follows:

import { Pipe, PipeTransform } from '@angular/core';  
@Pipe({name: 'Pipename'}) 

export class Pipeclass implements PipeTransform { 
   transform(parameters): returntype { } 
}

Where,

'Pipename' is the name of the pipe.

‘Pipeclass’ is the name of the class assigned to the custom pipe.

‘Transform’ is the function to work with the pipe.

‘Parameters’ are the parameters which are passed to the pipe.

‘Returntype’ the return type of the pipe.

29. Give an example of a custom pipe?

Let us now have a look at the example below where we have declared a custom pipe to convert a number to its square in the Angular application. Please note that we are using ng generate pipe command to create this custom pipe.

ng generate pipe square

// Output
CREATE src/app/square.pipe.spec.ts (187 bytes)
CREATE src/app/square.pipe.ts (217 bytes)
UPDATE src/app/app.module.ts (2931 bytes)

30. What is the difference between pure and impure pipe?

Basis Pure Pipe Impure Pipe
Meaning A pure pipe is called when a change in the value or the parameters passed to a pipe is detected by Angular.

 

An impure pipe is called in case of every change detection cycle irrespective of any change in the value or parameter passed.

 

Syntax @Pipe({

name: ‘filterPipe’,

pure: true

})

export class FilterPipe {}

@Pipe({

name: ‘filterPipe’,

pure: false

})

export class FilterPipe

Shareability Pure pipes can be shared across various usages and that too without having any effect on the output result Impure Pipes cannot be shared because they might affect the internal state from outside
Determination of Output change. Input values or parameters can determine the output value or the change in it. Input values cannot determine the output value or the change in it.

31. What is a bootstrapping module?

In Angular, the root module used for bootstrapping or launching the application is known as the ‘Bootstrapping Module’. A Bootstrapping Module is present in every Angular app and it is stored in the AppModule class. Infact, the Bootstrapping module is also called the AppModule.

32. Explain how to use HttpClient with an example?

The following are the generally followed steps to use the HttpClient :

  • Firstly, start by creating a HttpClient instance.
  • Next, create an instance of one of the methods.
  • Command HttpClient to execute the method.
  • After the execution, read the response.
  • Finally, release the connection.
  • And deal with the response.

33. How can you read the full response?

In order to read the full response in Angular, the following code should be used:

getUserResponse(): Observable<HttpResponse> {
  return this.http.get(
    this.userUrl, { observe: 'response' });
}

34. How do you perform Error handling?

In Angular, error handling can be done by writing a function using HttpClient along with catchError from RxJS.To handle errors, Angular’s HttpClient parses JSON responses and returns a JavaScript object in the observable.

35. What is content projection?

In Angular, Content projection refers to a pattern where you can insert, or project, the content you want to use inside a different component. For example, consider a Card component which can accept the content provided by another component.

36. What is the difference between promise and observable?

Basis Observables Promise
Values Observables have the capacity to emit multiple values over a given period of time. A promise emits only a single value over a given period of time.
Execution They can be executed only when subscribed using subscribe() method. Promises can be executed as soon as they get created.
Cancellation Observables are cancellable as they consist of subscriptions that can be cancelled using the unsubscribe() method. Promises once executed are non cancellable.
Operations Can provide operations like map for forEach, filter, reduce, retry, and retryWhen operators. Promises do not offer any operations.
Errors An observable pushes the errors to the subscribers A promise pushes the errors to the child promises.

37. What do you mean by data binding?

Data binding is among the most important and powerful features that help in establishing communication between DOM and the component. It makes the defining process of interactive applications simple as you no longer need to panic about data pushing or pulling between the component and the template.

Listed below are the four types of data binding in Angular:

  • Event binding
  • Property binding
  • String interpolation
  • Two-way data binding

38. What are some disadvantages of using Angular?

Although Angular provides quite a lot of benefits, there are some disadvantages of using it as well. They are as follows:

  • Getting good SEO results on an Angular application can be a bit difficult and may need a bit of configuration.
  • Angular has a lot of features packed into it, so getting to know each of them and learning how to use them effectively together can be a little difficult.
  • Angular can add quite a lot of weight to your JavaScript bundle, so using it for smaller projects can be very inefficient and may significantly increase the load size.

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39. What do you mean by string interpolation?

String interpolation in Angular, also known as the mustache syntax, only allows one-way data binding. It is a special syntax that makes use of double curly braces {{}} so that it can display the component data. Inside the braces are the JavaScript expressions that Angular needs to execute to retrieve the result, which can further be inserted into the HTML code. Moreover, as part of the digest cycle, these expressions are regularly updated and stored.

40. What are the differences between Angular decorator and annotation?

In Angular, decorators are design patterns that help in the modification or decoration of the respective classes without making changes in the actual source code.

Annotations, on the other hand, are used in Angular to build an annotation array. They use the Reflective Metadata library and are a metadata set of the given class.

41. What is an AOT compilation in Angular?

The AOT (ahead-of-time) compiler in Angular converts Angular HTML and TypeScript code into JavaScript code during the build phase, which makes the rendering process much faster. This compilation process is needed since Angular uses TypeScript and HTML code. The compiler converts the code into JavaScript, which can then be effectively used by the browser that runs our application.

42. What are the advantages of AOT?

AOT compilation has several advantages as mentioned below:

Fast rendering: Since, after compilation, the browser would download a pre-compiled version of our application, it can render the application immediately without compiling the app.

Less asynchronous requests: It takes external HTML templates and CSS style sheets and inlines them within the application JavaScript, which reduces the number of separate Ajax requests.

Smaller download size: The compiler will minify the code for us so that the download size is less.

Template error detection: During the compilation phase, any issues in the templates will be detected and reported by the compiler so that they can be corrected before production.

43. What are the three phases of AOT?

The three phases of AOT are:

  • code analysis
  • code generation
  • template type checking

44. What are the components in Angular?

Components are the basic building block of the user interface in Angular. A component consists of HTML, CSS, and JavaScript for a specific portion of a user interface. We can think of these as a custom HTML element that only Angular can understand. These components are isolated, i.e., styles and code from one component do not affect other components as they get namespaced by the compiler. These components are then pieced together by the Angular framework to build the user interface for the browser to render.

45. What are dynamic components?

Dynamic Components in the Angular framework are the components that help in building large-scale applications easily. Dynamic components are usually instantiated and placed in the application at runtime.

46. What is the purpose of base href tag?

The href attribute is used to specify the base URL for all relative URLs on a page.During navigation, the base href tag is used by the Angular router as a base path to the component, template, and module files.

47. What are modules in Angular?

A module is a logical boundary of our application. It is used to encapsulate code dealing with a specific aspect of the application, such as routing, HTTP, validation, etc. The main reason why modules are used is to enhance application composability. For example, if we wish to implement validation logic using different libraries, then for the one we have already implemented, we can create a new validation module and replace the current one with the new one, and our application would work just the same. In Angular, we create a module using the NgModule decorator.

48. What is DOM?

The full form of DOM is Document Object Model, and it is responsible for representing the content of a web page and changes in the architecture of an application. Here, all the objects are organized in the form of a tree, and the document can easily be modified, manipulated, and accessed only with the help of APIs.

49. What are services in Angular?

A service in Angular is a term that covers broad categories of functionalities. A service is any value, function, or feature that an app needs. A service is typically used to accomplish a very narrow purpose such as HTTP communication, sending data to a cloud service, decoding some text, validating data, etc. A service does one thing and does it well. It is different from a component as it is not concerned with HTML or any other kind of presentation logic. Normally, a component uses multiple services to accomplish multiple tasks.

50. What is the difference between jQuery and Angular?

The main difference between jQuery and Angular is that jQuery is a JS library, whereas Angular is a JS frontend framework. Some of the other differences between the two are mentioned below:

  • Unlike jQuery, Angular offers two-way data binding
  • Unlike Angular, jQuery does not offer support for the RESTful API
  • Angular supports deep linking routing, while jQuery does not
  • Form validation is available in Angular but not in jQuery

Although they have their differences, Angular and jQuery also have their set of similarities, like both jQuery and Angular expressions consist of variables, operators, and literals.

51. What are lifecycle hooks in Angular?

When building an Angular app, there will be times when we need to execute some code at some specific event—such as when a component is initialized or displayed on the screen or when the component is being removed from the screen. This is what lifecycle hooks are used for. For example, if we have some event listener attached to an HTML element in a component, such as a button click or form submission, we can remove that event listener before removing the component from the screen, just like we can fetch some data and display it on the screen in a component after the component is loaded on the screen. To use a lifecycle hook, we can override some methods on a component, such as ngOnInit or ngAfterViewInit. These methods, if available on a component, will be called by Angular automatically. This is why these are called lifecycle hooks.

52. What are templates?

Angular templates are written using HTML that includes attributes and elements that are specific to Angular. The templates are further combined with the data from the controller and the model, which can be rendered to offer the user a dynamic view.

53. What is a two-way data binding?

Two-way data binding is done in Angular to ensure that the data model is automatically synchronized in the view. For example, when a user updates some data in a model and that model is being displayed in multiple places in a component, that update should be reflected in all the places.

Two-way data binding has been supported in Angular for a long time. Although, it is something that should be used with careful consideration as it could lead to poor application performance or performance degradation as time goes on. It is called two-way data binding because we can change some data that is in the component model from the view that is HTML, and that change can also propagate to all other places in the view where it is displayed.

Looking to get started with AngularJS? Head on to our blog on AngularJS tutorial!

54. What are pipes in Angular?

When we are trying to output some dynamic data in our templates, we may sometimes need to manipulate or transform the data before it is put into our templates. Though there are several ways of doing that, in Angular, using pipes is the most preferred way. A pipe is just a simple function, which we can use with expressions in our templates.

Pipes are extremely useful as we can use them throughout our application after declaring them just once and registering them with the Angular framework. Some of the most common built-in pipes in Angular are UpperCasePipe, LowerCasePipe, CurrencyPipe, etc.

55. What are observables in Angular?

An observable is a declarative way using which we can perform asynchronous tasks. Observables can be thought of as streams of data flowing from a publisher to a subscriber. They are similar to promises as they both deal with handling asynchronous requests. However, observables are considered to be a better alternative to promises as the former comes with a lot of operators that allow developers to better deal with asynchronous requests, especially if there is more than one request at a time.

Observables are preferred by many developers as they allow them to perform multiple operations such as combining two observables, mapping an observable into another observable, and even piping multiple operations through an observable to manipulate its data.

56. How are observables different from promises?

Although both promises and observables are used to handle asynchronous requests in JavaScript, they work in very different ways. Promises can only handle a single event at a time, while observables can handle a sequence of asynchronous events over a period of time. Observables also provide us with a wide variety of operators that allow us to transform data flowing through these observables with ease.

A promise is just a way to wrap asynchronous operations so that they can be easily used, while an observable is a way to turn asynchronous operations into a stream of data that flows from a publisher to a subscriber through a well-defined path with multiple operations transforming the data along the way.

57. What does Angular Material mean?

Angular Material is a UI component library that allows professionals to develop consistent, attractive, and completely functional websites, web pages, and web applications. It becomes capable of doing so by following modern principles of web designing, such as graceful degradation and browser probability.

58. What is RxJS?

RxJS is a library, and the term stands for Reactive Extensions for JavaScript. It is used so that we can use observables in our JavaScript project, which enables us to perform reactive programming. RxJS is used in many popular frameworks such as Angular because it allows us to compose our asynchronous operations or callback-based code into a series of operations performed on a stream of data that emits values from a publisher to a subscriber. Other languages such as Java, Python, etc. also have libraries that allow them to write reactive code using observables.

Angular Intermediate Questions

59. What is bootstrapping?

Angular bootstrapping, in simple words, allows professionals to initialize or start the Angular application. Angular supports both manual and automatic bootstrapping. Let’s briefly understand the two.

  • Manual bootstrapping: It gives more control to professionals with regards to how and when they need to initialize the Angular app. It is extremely useful in places where professionals wish to perform other tasks and operations before the Angular compiles the page.
  • Automatic bootstrapping: Automatic bootstrapping can be used to add the ng-app directive to the application’s root, often on the tag if professionals need Angular to automatically bootstrap the application. Angular loads the associated module once it finds the ng-app directive and, further, compiles the DOM.

Want to learn more about Angular Bootstrap? Check out our Angular Bootstrap Tutorial!

60. What do you mean by dependency injection?

Dependency injection (DI) in Angular is a software design pattern in which the objects can be passed in the form of dependencies instead of hard-coding them in the respective components. This concept is extremely handy when it comes to separating the object logic creation from its consumption.

The function ‘config’ uses DI that needs to be configured so that the module can be loaded to retrieve the application elements. Besides, this feature allows professionals to change dependencies based on necessities.

61. What are Angular building blocks?

The following building blocks play a crucial role in Angular:

  • Components: A component can control numerous views wherein each of the views is a particular part on the screen. All Angular applications have a minimum of one component called the root component. This component is bootstrapped in the root module, the main module. All the components include the logic of the application that is defined in a class, while the main role of the class is to interact with the view using an API of functions and properties.
  • Data binding: Data binding is the process in which the various sections of a template interact with the component. The binding markup needs to be added to the HTML template so that Angular can understand how it can connect with the component and template.
  • Dependency injection: It uses DI so that it can offer the necessary dependencies, mainly services, to the new components. The constructor parameters of a component inform Angular regarding the numerous services needed by the component, and DI provides a solution that gives the necessary dependencies to the new class instances.
  • Directives: Angular templates are of dynamic nature, and directives help Angular understand how it can transform the DOM while manifesting the template.
  • Metadata: Classes have metadata attached to them with the help of decorators so that Angular will have an idea of processing the class.
  • Modules: Module or NgModule is a block of code organized using the necessary capabilities set, having one specific workflow. All Angular applications have at least one module, the root module, and most of the applications have numerous modules.
  • Routing: Angular router helps interpret the URL of a browser to get a client-generated experience and view. This router is bound to page links so that Angular can go to the application view as soon as the user clicks on it.
  • Services: Service is a vast category that ranges from functions and values to features that play a significant role in Angular applications.
  • Template: The view of each component is linked with a template, and an Angular template is a type of HTML tag that allows Angular to get an idea of how it needs to render the component.

62. Explain the MVVM architecture.

The MVVM architecture plays a significant role in eliminating tight coupling between the components. This architecture includes the following three parts:

  • Model: The model represents the business logic and data of a particular application. In other words, it consists of an entity structure. The model has the business logic, including model classes, remote and local data sources, and the repository.
  • View: View is the application’s visual layer that comprises the UI code. The view sends the action of the user to the ViewModel. However, it does not receive the response directly. The view must subscribe to the observables that are exposed to it by the ViewModel to receive a response.
  • ViewModel: ViewModel is the application’s abstract layer that connects the View and the Model and acts as a bridge between the two. It does not know which View needs to be made use of since it does not have any direct access to the View. The two are connected using data binding, and the ViewModel records all the changes that are made to the View and makes the necessary changes to the Model.

63. Describe Angular authentication and authorization.

The login details of a user are given to an authenticate API available on the server. Once the credentials are validated by the server, it returns a JSON web token (JWT), which includes attributes and the data of the current user. Further, the user is easily identified using JWT, and this process is known as authentication.

After logging in, users have various types and levels of access—some can access everything, while others may have restrictions from some resources. Authorization determines the access level of these users.

64. What is the digest cycle process in Angular?

Digest cycle in Angular is the process in which the watch list is monitored to track changes in the watch variable value. In each digest cycle, there is a comparison between the present and the previous versions of the scope model values.

65. What are the distinct types of Angular filters?

Filters are a part of Angular that helps in formatting the expression value to show it to the user. They can be added to services, directives, templates, or controllers. You also have the option to create personalized filters as per requirements. These filters allow you to organize the data easily such that only the data that meets the respective criteria are displayed. Filters are placed after the pipe symbol ( | ) while used in expressions.

Various types of filters in Angular are mentioned below:

currency: It converts numbers to the currency format

filter: It selects a subset containing items from the given array

date: It converts a date into a necessary format

lowercase: It converts the given string into lowercase

uppercase: It converts the given string into uppercase

orderBy: It arranges an array by the given expression

json: It formats any object into a JSON string

number: It converts a number value into a string

limitTo: It restricts the limit of a given string or array to a particular number of elements or strings

66. How can one create a service in Angular?

Service in Angular is an object that can be substituted. It is wired and combined with the help of dependency injection. Services are developed by getting registered in a module that they need to be executed in. The three methods of creating a service in Angular are as follows:

  • Service
  • Factory
  • Provider

Angular Advanced Level Questions

67. What does subscribing mean in RxJS?

In RxJS, when using observables, we need to subscribe to an observable to use the data that flows through that observable. This data is generated from a publisher and is consumed by a subscriber. When we subscribe to an observable, we pass in a function for the data and another function for errors so that, in case there is some error, we can show some message or process the message in some way.

68. What is Angular Router?

Routing in a single-page frontend application is the task of responding to the changes in the URL made by adding and removing content from the application. This is a complicated task as we first need to intercept a request that changes the browser’s URL as we do not wish for the browser to reload. Then, we need to determine which content to remove and which content to add, and finally, we have to change the browser’s URL as well to show the user the current page they are on.

As we can see, this can be very difficult to implement, especially in multiple applications. That is why Angular comes with a full routing solution for a single-page application. In this, we can define routes with matching components and let Angular handle the routing process.

69. What is REST?

REST in Angular stands for Representational State Transfer. It is an API that works on the request of HTTP. Here, the requested URL points to the data that has to be processed, after which an HTTP function is used to identify the respective operation that has to be performed on the data given. The APIs that follow this method are referred to as RESTful APIs.

70. What is the scope?

A scope is an object in Angular referring to the application model. It is a context for executing expressions. These scopes are organized in a hierarchical form that is similar to the application’s DOM structure. A scope helps in propagating various events and watching expressions.

71. Explain Angular CLI.

Angular CLI is otherwise known as Angular command-line interface. Angular supports CLI tools that give professionals the ability to use them to add components, deploy them instantly, and perform testing and many such functions.

72. How do you create directives using CLI?

To create a directive using Angular CLI, the following steps are used:

  • Start a new project using Angular CLI through the following command:
‘ng new [application-name]’
  • Now change the directory into a new directory through the command:
‘cd [application-name]’
  • Once done with changing the directory, use the following command to generate a new directive:
‘ng generate directive [path-to-directives/my-directive]’

73. What is schematic?

Schematics are template-based code generators that enable complex logic. It is usually packaged into collections and installed with npm. The aim of schematics is to transform a software project by generating or modifying codes.

74. What is a rule in Schematics?

Rule in Schematic refers to a set function that takes a Tree, transforms it and finally returns a new Tree.

78. What is Schematics CLI?

Schematics CLI is used to transform web-based applications projects.

79. What is HttpClient, and what are its benefits?

HttpClient is an Angular module used for communicating with a backend service via the HTTP protocol. Usually, in frontend applications, for sending requests, we use the fetch API. However, the fetch API uses promises. Promises are useful, but they do not offer the rich functionalities that observables offer. This is why we use HttpClient in Angular as it returns the data as an observable, which we can subscribe to, unsubscribe to, and perform several operations on using operators. Observables can be converted to promises, and an observable can be created from a promise as well.

80. What is multicasting in Angular?

In Angular, when we are using the HttpClient module to communicate with a backend service and fetch some data, after fetching the data, we can broadcast it to multiple subscribers, all in one execution. This task of responding with data to multiple subscribers is called multicasting. It is specifically useful when we have multiple parts of our applications waiting for some data. To use multicasting, we need to use an RxJS subject. As observables are unicast, they do not allow multiple subscribers. However, subjects do allow multiple subscribers and are multicast.

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81. What is a directive in Angular?

A directive in Angular is used to extend the syntax and capabilities of a normal HTML view. Angular directives have special meaning and are understood by the Angular compiler. When Angular begins compiling the TypeScript, CSS, and HTML files into a single JavaScript file, it scans through the entire code and looks for a directive that has been registered. In case it finds a match, then the compiler changes the HTML view accordingly.

Angular is shipped with many directives. However, we can build our directives and let Angular know what they do so that the compiler knows about them and uses them during the compilation step.

82. What will happen if you do not supply handler for observer?

When a handler is not supplied to a notification type, the observer automatically ignores the notifications of that type and the observer instance publishes value only when it is subscribed to.

83. What are angular elements?

Angular elements refer to the Angular components that are a web standard for defining new HTML elements and are packed as custom elements. These custom elements are also called Web Components. The Angular custom elements bootstrap automatically when added to the DOM tree.

84. What is the browser support of Angular Elements?

Since Angular is built on the latest web platform standards, Angular elements are supported by Chrome, Edge (Chromium-based), Firefox, Opera, and Safari and other currently existing browsers via polyfills.Polyfills enable the running of full Angular applications.

85. What is the role of SPA in Angular?

SPA stands for Single Page Application. This technology only maintains one page, index.HTML, even when the URL changes constantly. SPA technology is easy to build and extremely fast in comparison to traditional web technology.

86. Explain different kinds of Angular directives.

There are three kinds of directives in Angular. Let’s discuss them:

  • Components: A component is simply a directive with a template. It is used to define a single piece of the user interface using TypeScript code, CSS styles, and the HTML template. When we define a component, we use the component decorated with the @ symbol and pass in an object with a selector attribute. The selector attribute gives the Angular compiler the HTML tag that the component is associated with so that, now, when it encounters this tag in HTML, it knows to replace it with the component template.
  • Structural: Structural directives are used to change the structure of a view. For example, if we wish to show or hide some data based on some property, we can do so by using the ngIf directive, or if we wish to add a list of data in the markup, we can use *ngFor, and so on. These directives are called structural directives because they change the structure of the template.
  • Attribute: Attribute directives change the appearance or behavior of an element, component, or another directive. They are used as the attributes of elements. Directives such as ngClass and ngStyle are attribute directives.

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87. What are the different types of compilers used in Angular?

In Angular, we use two different kinds of compilers:

  • Just-in-time (JIT) compiler
  • Ahead-of-time (AOT) compiler

Both these compilers are useful but for quite different purposes. The JIT compiler is used to compile TypeScript to JavaScript as our browsers cannot understand TypeScript but only JavaScript. This compilation step is done in a development environment, i.e., when less time is needed to be spent on compilation and more in development to quickly iterate over features. The JIT compiler is used when we use ng serve or ng build command to serve the app locally or create an uncompressed build of the entire codebase.

On the other hand, the AOT compiler is used to create a minified production build of the entire codebase, which can be used in production. To use the AOT compiler, we have to use the ng build command with the –prod blog: ng build –prod. This instructs the Angular CLI to create an optimized production build of the codebase. This takes a bit more time because several optimizations such as minification can take time, but for production builds, this time can be spared.

88. What is the purpose of the common module in Angular?

In Angular, the common module that is available in the package @angualr/common is a module that encapsulates all the commonly needed features of Angular, such as services, pipes, directives, etc. It contains some sub-modules as well such as the HttpClientModule, which is available in the @angular/common/http package. Because of the modular nature of Angular, its functionalities are stored in small self-contained modules, which can be imported and included in our projects if we need these functionalities.

Read the differences Angularjs, Angular 2 and Angular 4 in our comparative blog on Angularjs vs Angular 2 vs Angular 4!

89. What are the differences between AngularJS and Angular?

AngularJS is the previous version of Angular, which is a complete rewrite, i.e., there are several differences between the two that we can highlight.

  • Architecture: AngularJS supports the MVC architecture in which the model contains the business logic; the view shows the information fetched from the models, and the controller manages interactions between the view and the model by fetching data from the model and passing it to the view. On the other hand, Angular architecture is based on components where instead of having separate pieces for logic, presentation, etc., we now have a single self-contained piece of the user interface that can be used in isolation or included in a big project.
  • Language: In AngularJS, we could only use JavaScript. However, in Angular, we can use both TypeScript and JavaScript.
  • Mobile support: In AngularJS, we do not get mobile browser support out of the box, but in Angular, we do get mobile support for all popular mobile browsers.

90. What are the differences between Angular expressions and JavaScript expressions?

Angular expressions and JavaScript expressions are quite different from each other as, in Angular, we are allowed to write JavaScript in HTML, which we cannot do in plain JavaScript. Also, all expressions in Angular are scoped locally. But, in JavaScript, these expressions are scoped against the global window object. These differences, however, are reconciled when the Angular compiler takes the Angular code we have written and converts it into plain JavaScript, which can then be understood and used by a web browser.

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91. What is server-side rendering in Angular?

In a normal Angular application, the browser executes our application, and JavaScript handles all the user interactions. However, because of this, sometimes, if we have a large application with a big bundle size, our page’s load speed is slowed down quite a bit as it needs to download all the files, parse JavaScript, and then execute it. To overcome this slowness, we can use server-side rendering, which allows us to send a fully rendered page from the server that the browser can display and then let the JavaScript code take over any subsequent interactions from the user.

92. What is Angular Universal?

Angular Universal is a package for enabling server-side rendering in Angular applications. We can easily make our application ready for server-side rendering using the Angular CLI. To do this, we need to type the following command:

ng add @nguniversal/express-engine

This allows our Angular application to work well with an ExpressJS web server that compiles HTML pages with Angular Universal based on client requests. This also creates the server-side app module, app.server.module.ts, in our application directory.

Check out this Angular tutorial video designed to help you better understand the Angular framework:

https://youtu.be/K5FL6-6Wmjw

93. What is the difference between interpolated content and the content assigned to the innerHTML property of a DOM element?

Angular interpolation happens when in our template we type some JavaScript expression inside double curly braces ‘{{ someExpression() }}’. This is used to add dynamic content to a web page. However, we can do the same by assigning some dynamic content to the innerHTML property of a DOM element. The difference between the two is that, in Angular, the compiler always escapes the interpolated content, i.e., HTML is not interpreted, and the browser displays the code as it is with brackets and symbols, rather than displaying the output of the interpreted HTML. However, in innerHTML, if the content is HTML, then it is interpreted as the HTML code.

94. What are HttpInterceptors in Angular?

HttpInterceptors are part of the @angular/common/HTTP module and are used to inspect and transform HTTP requests and HTTP responses as well. These interceptors are created to perform checks on a request, manipulate the response, and perform cross-cutting concerns, such as logging requests, authenticating a user using a request, using gzip to compress the response, etc. Hopefully, these Angular interview questions in 2021 have helped you get a better grasp of Angular as a framework, as well as its various features and capabilities. These frequently asked questions have been created to give you a better understanding of the kinds of questions asked in interviews, so they will help you in understanding Angular interviews and Angular as a framework. These Angular interview questions with their answers might have whetted your appetite for learning more about the framework. They will surely help you to ace your next job interview.

95. How does one share data between components in Angular?

There is not one but various methods to share data between components in Angular. They are mentioned as below:

  • Parent to Child: via Input
  • Child to Parent: via Output() and EventEmitter
  • Child to Parent: via ViewChild
  • Unrelated Components: via a Service

96. What is ng-content and its purpose?

The usage of ng-content in Angular is to insert the content dynamically inside the component. It helps in  increasing component reusability and passing content inside the component selector.

97. What is ngcc?

The ngcc(Angular Compatibility Compiler) is a tool used in Angular to upgrade node_module, compiled with non-ivy ngc into ivy compliant format.

98. What is folding?

In Angular, it might be possible while generating the code that some of the non-exported members are folded. This is called Folding, i.e the process in which the evaluation of an expression is done by the collector and result is recorded in the .metadata.json, is known as Folding.

99. What are macros?

A Macros is a portion of a  programming code that helps in the automation of routine tasks. It usually runs in an excel environment. In Angular, Macros is supported in the form of functions, static methods etc. Consider the below example of a Macros code in Angular :

export function wrapInArray<T>(value: T): T[] {
return [value];
}

100. What is the State function?

The State function in Angular declares an animation state within a trigger attached to an element. The following is the syntax for State function:

state(name: string, styles: AnimationStyleMetadata, options?: { params: { [name: string]: any; }; }): AnimationStateMetadata

101. What is Style function?

The Style function in Angular is used to declare a key/value object that contains CSS properties/styles and are used for an animation. The syntax of the Style function is given by:

style(tokens: "*" | { [key: string]: string | number; } | ("*" | { [key: string]: string | number; })[]): AnimationStyleMetadata

102. What is NgZone?

NgZone is a service provided by Angular that allows you to execute functions in the Angular zone through a run() method. This execution is carried out when NgZone triggers change detection automatically at the right time.

export class AppComponent implements OnInit {
constructor(private ngZone: NgZone) {}
ngOnInit() {
// New async API is not handled by Zone, so you need to use ngZone.run()
// to make the asynchronous operation callback in the Angular zone and
// trigger change detection automatically.
someNewAsyncAPI(() => {
this.ngZone.run(() => 
// update the data of the component
});
});
}
}

103. What is NoopZone?

NoopZone helps Angular figure out and know when to trigger the change detection. However, in the event when Angular needs to be used without a zone, the NoopZone too needs to be configured.

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2 thoughts on “Top 100+ Angular Interview Questions and Answers 2022”

  1. Very good collection of questions and answers, loved the diversified nature of questions collections covering different areas.

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