Top 50 Angular Interview Questions & Answers

30-Aug-2022

Angular is amongst the most popular development platforms. It is an application framework with a single-page framework. Companies and organizations nowadays are competing to take advantage of the benefits of the Angular platform for which they are increasingly hiring experts in Angular. Angular is vast and has a high level of difficulty in navigating.  The Angular ecosystem is made up of a varied community of more than 1.7 million developers, library authors, and content producers, which is the best part. Hence, it is also difficult to get through an Angular interview. However, referring to some of the top angular interview questions & answers will help you have a smooth interview. We have curated the most frequently asked angular interview questions & answers to help you familiarize yourself with the most fundamental concepts and sets of questions. The following top Angular interview questions and answers are categorized based on the knowledge levels from basic to advanced.

Angular Interview Questions & Answers at Basic Level

1. What is Angular?

Google developed the open-source Angular web application development framework. It is used to create frontend, single-page JavaScript apps. It is a complete framework, which means that it handles numerous frontend web application components including HTTP requests, layout, forms, reactivity, routing, validation, etc.

2. What Technologies are Employed by Angular?

Google created the cutting-edge JavaScript frontend framework known as Angular. For several reasons, including to make sure activities are easier to do and to give developers a better experience while using it to create apps, Angular itself uses a variety of technologies. TypeScript, a superscript of JavaScript, is used by Angular. Any legitimate JavaScript is thus a legitimate TypeScript. However, TypeScript enables us to write JavaScript as a tightly typed language and gives us the ability to define our own types, making it much simpler to find issues. It also makes use of RxJS, which enables programmers to handle asynchronous processes more effectively.

3. What Gave Rise to the Introduction of Client-side Frameworks like Angular?

Dynamic websites used to function by accepting a template that was nothing but HTML code with gaps left vacant for feeding data and content into those templates before JavaScript-based client-side frameworks. Typically, a database was used to retrieve this data. We would serve the user the created HTML content after integrating the template and data. As you can see, it was somewhat difficult and required a lot of processing in some instances.

To get over these problems, people developed a different strategy where they deliver the information a website needs to render from their web servers to the browsers and let JavaScript mix it with a pre-made template. The servers can now simply deliver the data to a client via the internet in a recognizable format, i.e., JSON, XML, etc., as even mobile phones can perform this kind of processing. Performance is enhanced and server processing is greatly reduced as a result.

4. How do Angular Applications Function?

The components of Angular are what makes it function. Therefore, the configuration file ANGULAR.JSON is where the Angular application gets started. This file is used by the builder to locate the main file, configurations, and paths. The procedure is now about to begin. The MAIN.TS file, which serves as the configuration file's entry point, is the next. In essence, it aids in building the browser environment needed for the application to run. Now, the APP.MODULE.TS is used to do the bootstrapping of the Angular application. 

The APP.COMPONENT.TS file now contains the bootstrapped app component. Now, Angular is asked to load the application component by calling the INDEX.HTML file. Following component loading, the APP.COMPONENT.HTML file is used to show the component's content. This is how the Angular application functions and the components we've spoken about here contribute to it.

5. Define TypeScript

TypeScript is a feature that comes in Angular which is favored by most Front-end Developers. It comes with an automatic populating function that helps in easy compilation and detecting of bugs effectively. TypeScript also facilitates reduction in the developing time with its rich interfaces, hybrid types, access modifiers, etc.

6. How will you write an Angular Architecture in a pictorial Diagram?

To represent an angular architecture in a pictorial diagram, the following elements are essential:

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

7. Describe Metadata

Metadata is used to instruct Angular on the procedures of handling a class. Unless we explicitly notify Angular that a component is being used, which we do with the aid of metadata, a component behaves as a class when it is used. A decorator is used in TypeScript to attach metadata. Decorators are functions that are familiar with the setup of classes and how they should operate.

8. Can you distinguish Constructor and ngOnIit?

We can differentiate Constructor from ngOnInit based on the following two aspects:

• Objective: While the primary goal of a Constructor is to start class members, ngOnInit on the contrary is employed in the event of starting or announcing and avoiding things for working in builders. 
• Usage: A constructor is used for setting up dependency injection and Initialization of class fields while ngOnInit is used for writing work code that operates soon after the instantiation of the class. 

9. What is the process of developing a Dependency Hierarchy?

Angular has a dependency injection that is hierarchical. It comprises an injection tree that is parallel to the component tree of the application. The configurations result in the formation of the dependency hierarchy. 

Any level of the component tree can be used to reconfigure the injectors. In the injector hierarchy, the suppliers for various injectors can also be specified.

10. What function does the async pipe serve?

The async pipe simply serves the purpose of marking the components that need to be checked for changes. It returns the most recent value it has emitted and subscribes to an Observable or Promise. The components are identified by the async pipe once this new value has been emitted. Now, the async pipe automatically detaches or unsubscribes if any component is deleted. 

Similar to this, the async pipe unsubscribes from the previous Observable or Promise and subscribes to the new one if the expression reference of the component changes.

11. What does the choice between an Inline and an External template entail?

Inline templates are typically utilized for shortcodes and external templates for somewhat large displays. However, company policy, conditions, etc., sometimes determine whether to use inline or external templates.

12. What does the ngFor directive do?

The ngFor directive is used whenever it is necessary to repeat a part or parts of an HTML template once for each item in a collection. In essence, it uses the ngFor directive to construct a template for each iteration as it gets simpler.

13. Can you highlight the purpose of the ngIF directive?

The ngIf directive's goal is to destroy or recreate a section of the DOM tree in accordance with an expression. The element is deleted from the tree if the ngIf directive determines that the expression is evaluated to be false; else, a matching element is added to the DOM tree.

14. What occurs if a script tag is used inside a template?

When a script tag is used inside a template, Angular flags the value as unsafe and starts the sanitization process on its own. This eliminates the script tag while protecting the text element's content. The risk of injection attacks is eliminated as a result of the entire process.

15. Define Template expressions

An expression that generates a value and is enclosed in double curly brackets is known as a template expression in Angular. Angular executes the template expression and applies it to a binding target property. Any of these—an HTML element, a directive, or even a component—can now be the binding target.

16. How do template statements work?

Template statements in Angular refer to the operations or elements that are used in HTML in response to user events. Through activities like the presentation of dynamic content or the submission of forms, among others, these template statements enable your application to engage users.

17. Can you differentiate between Angular and AngularJS?

To differentiate Angular and AngularJS, the following features can be used for comparison:

• Architecture: While Angular applies components and directives AngularJS supports the MVC (Model-View-Controller) model.  
• Language: Angular uses a superset of JavaScript which is typed statistically particularly TypeScript, on the other hand, AngularJs uses JavaScript which is a dynamically typed language. 
• Expression Syntax: Angular makes use of () for binding an event and [] for binding a property. On the contrary, in AngulaJS, for using an accurate ng directive for binding an event or a property requires professionals. 
• Mobile Support: While Angular offers mobile supportAngularJS does not.
• Routing: While Angular uses @RouteConfig{(…)}, AngularJs uses $routeprovider.when()
• Dependency Injection: Angular supports dependency injection in hierarchy coupled with a unidirectional tree-based change direction,  AngularJs does not support dependency injection
• Structure: Angular's simplified structure facilitates professionals with easy development and maintenance of large applications, AngularJs is relatively less manageable. 

18. What are the benefits of Angular use?

There are various benefits to using Angular, which are detailed below:

• Because TypeScript is used in the development of Angular, programmers can write tightly typed code that will be translated into JavaScript. Strongly typed code has the advantages of being simple to read, manageable, and less error-prone. Additionally, it offers improved tooling, including type hints and code completion.
• With the help of Angular, we can divide our code into modules that may be used to encapsulate functionality associated with a particular activity, such as HTTP connection, data validation, routing, etc.
• A vast ecosystem of Angular's tools, libraries, frameworks, plugins, and other components speed up and improve the development process overall. RxJS, NgRx, Angular CLI, and other programs and libraries are among them.

19. Can you explain the types of data binding?

Data binding in Angular is categorized into many categories. The types of data binding in Angular are as follows:

One-way Binding: Changes in the state have an impact on the view from the component to the view template in one-way data binding. On the other hand, it's also feasible that a view's transformation from a view template to a component will have an impact on the state.

Two-way Binding: With regard to two-way data binding, modifications made to the view may result in model modifications. In a similar vein, any model modifications could convert the view from a component to a view template.

The numerous types under Two-way Binding are:

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

20. Explain parameterized pipe

Before the data is finally displayed to the end users, Angular uses pipes to transform the raw data into the necessary format. In general, there are two categories for these pipes: Internal Pipes and Personalized Pipes.

The two forms of built-in pipes are parameterized pipes and chaining pipes. Pipes that contain parameters are referred to as parameterized pipes. With the use of a colon (:) in the command, we may use these pipes to pass an unlimited amount of parameters.

21. What are custom elements, exactly?

You can design a tag whose content is generated and managed by JavaScript code using a custom element to expand HTML.

22. Do I need to use custom Bootstrap elements?

The answer is no, you don't need to bootstrap custom elements because they do so when they are added to the DOM. Additionally, Angular's custom elements are automatically destroyed when they are removed from the DOM.

23. Is it a necessity to use custom Bootstrap elements?

The answer is no, you don't need to bootstrap custom elements because they do so when they are added to the DOM. Additionally, Angular's custom elements are automatically destroyed when they are removed from the DOM.

24. How do the internal workings of custom elements work?

The following is the step-by-step information on the internal operation of custom elements step by step:

• Registration of the custom elements: Angular uses the createCustomElement() function to register the custom elements. This procedure turns a component into a class that can be registered as a custom element with the browser. 
• The custom element is added to the DOM in a manner similar to built-in HTML is added. 
• A registered class is instantiated by the browser and added to the DOM once the custom element has been introduced to the document object model(DOM)
• Data binding and change detection are enabled in the last stage by the newly created instance. Utilizing the component, the template's content is rendered and DOM data. 

25. How can components be converted into bespoke elements?

Transferring components to custom elements requires two crucial procedures to be taken:

• Developing a custom element class: To begin, use Angular's createCustomElement() function to generate a custom element class. An Angular component (together with any dependencies it may have) is converted to a custom element by the function. Through this conversion, the NgElementConstructor interface is implemented, resulting in a function Object() { [native code] } class that can be used to produce a self-bootstrapping instance.
• Element class registration with the browser: The configured function Object() { [native code] } and the corresponding custom-element tag are registered with the browser's CustomElementRegistry using the customElements.define() function.

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

The following list contains the key mapping rules between an Angular component and a custom element:

• Using the createCustomElement() API, the component input properties are processed with the appropriate attributes for the custom element.
• The outputs from components are sent as HTML Custom Events with names that are identical to the output names.

27. What are custom pipes?

With Angular, you can build unique pipes. They were once referred to as "Filters" in Angular and are nothing more than specialized pipes.

28. Describe bootstrapping module.

The "Bootstrapping Module" in Angular is the root module used to launch or bootstrap the application. Every Angular project contains a Bootstrapping Module, which is kept in the AppModule class. In actuality, the AppModule is another name for the Bootstrapping module.

29. How is error handling carried out?

Error handling in Angular may be accomplished by creating a function that uses RxJS's catchError and HttpClient's caatchError. The HttpClient in Angular parses JSON replies and returns a JavaScript object in the observable to handle problems.

30. Explain Content Projection?

The term "Material projection" in the context of Angular refers to a pattern where you can project the content you wish to use within another component. Consider a card component, for instance, which may accept content from another component.  

31. Can you give an example of how to utilize HttpClient?

The actions that are typically taken when using HttpClient are as follows:

• Make an instance of the HttpClient first.
• Then follow up by creating a method instance should then be created.
• To run the method, issue the HttpClient command.
• Read the response after the execution.
• Release the connection at the end.
• Finally, respond to the reply.

 32. How will you differentiate Promise from Observable?

We can differentiate Promise from Observable by taking into consideration of the following basis:

• Values: While observables can emit several values over a stipulated time period, Promise can only emit a single value in a designated time. 
• Execution: Observables are only applied when subscribed by using the subscribe () method. While the execution of a Promise can be made soon after theri creation.       
• Cancellation: While observables have the option of cancellation as they have a subscription by executing the unsubscribe() method, Promises are not cancellable. 
• Operations:  Observables offer numerous operations like filter, retry, map forEach, retrywhen, etc. On the contrary, such offers are not available with Promises. 
• Error: With observables, errors are pushed to the subscribers but with promises, the errors are pushed to the child promises.

33. Explain Data Binding?

One of the most significant and potent aspects that aid in creating communication between the DOM and the component is data binding. Since there is no longer a need to worry about data pushing or pulling between the component and the template, it simplifies the process of developing interactive applications.

The four types of data binding in Angular are listed below:

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

34. What are the drawbacks of Angular usage?

Although utilizing Angular has a lot of advantages, there are some drawbacks as well. These are what they are:

• On an Angular application, getting decent SEO results can be challenging and may require some configuration.
• Because Angular offers so many features, it can be challenging to get to know them all and figure out how to use them well together.
• Using Angular for smaller projects can be quite inefficient and may dramatically increase the load size because it can add a large amount of weight to your JavaScript bundle.

35. What exactly does string interpolation mean?

The Moustache syntax, also known as string interpolation, in Angular only permits one-way data binding. Double curly braces are used in a particular syntax for this purpose so that the component data can be displayed. The JavaScript expression that Angular must run to acquire the result is included within the brackets and can then be put into the HTML code. Additionally, these expressions are consistently updated and saved as part of the digest cycle. 

36. What distinguishes an Angular decorator from an annotation?

Decorators in Angular are design patterns that assist in modifying or beautifying the relevant classes without altering the real source code.

On the other side, Angular uses annotations to create an annotation array. They are a set of metadata for the specified class and make use of the Reflective Metadata library.

37. What in Angular is an AOT compilation?

The rendering process is significantly sped up by Angular's AOT (ahead-of-time) compiler, which transforms Angular HTML and TypeScript code into JavaScript code during the development phase. Due to the use of TypeScript and HTML code by Angular, this compilation procedure is required. The compiler transforms the code into JavaScript so that the browser running our application can make use of it.

38. What benefits does AOT offer?

The following are the benefits that AOT compilation offers:

• Fast rendering: Since the browser would download a pre-compiled version of our application after compilation, it is possible to render it right away without the need for compilation.
• Less asynchronous requests: It embeds external CSS and HTML stylesheets into the JavaScript of the application, reducing the amount of individual Ajax queries.
• Smaller download sizes will result from the compiler's minification of the code.
• Template error detection: Any errors in the templates will be found and reported by the compiler during the compilation step so they may be fixed before production.

39. What are the phases involved in AOT?

The following are the three different phases of AOT:

• code analysis
• code generation
• template type checking

40. What do the Angular components look like?

The fundamental unit of the Angular area of a user interface is made up of HTML, JavaScript, and CSS. These can be compared to a unique HTML element that only Angular can comprehend. As the compiler namespacing 

them, these components are isolated, so styles and code from one component do not influence other components. The Angular framework then assembles these parts to create the user interface that the browser will display.

41. Describe Dynamic elements?

The Angular framework's dynamic components are the components that make it simpler to create complex applications. Typically, dynamic elements are instantiated and added to the program at runtime. 

42. What does the base href tag do?

All relative URLs on a page must have a base URL, which is specified by the href attribute. The base href tag serves as a base path to the component, template, and module file during navigation by the Angular router. 

43. What do ANgular Modules do?

A logical boundary of an application is a module. Code dealing with a particular area of the program, such as routing, HTTP, validation, etc., is contained within it. The primary goal of using modules is to improve application composability. For instance, if we wanted to develop validation logic using different libraries, we could create a new validation module and swap out the old one for the existing one. The application would still function as intended. Using the NgModule decorator, we build a module in Angular.

44. What is DOM? 

It simply means Document Object Model which is in charge of expressing changes in an application's architecture as well as the content of a web page. The document can only be easily edited, manipulated, and accessed with the aid of APIs in this case because all the objects are arranged in the shape of a tree. 

45. What do the Angular services mean? 

In Angular, the term "service" refers to a broad category of functionality. Any benefit, feature, or capability that an app requires is a service. A service is often employed to carry out a very specific task, such as HTTP communication, data transmission to a cloud service, text decoding, data validation, etc. A service just performs one task but does it well. Since it is not concerned with HTML or any other form of presentation logic, it differs from a component. A component typically makes use of several services to complete a variety of activities.

46. What distinguishes jQuery and Angular from one another?

The primary distinction between jQuery and Angular is that the latter is a JS frontend framework and the former is a JS library. Below are a few further distinctions between the two:

• Angular provides two-way data binding, in contrast to jQuery.
• jQuery does not provide support for the RESTful API, in contrast to Angular.
• While jQuery does not enable deep linking routing, Angular does.
• In contrast to jQuery, Angular offers form validation.
• Angular and jQuery differ from one another, but they also share a number of commonalities, such as the fact that both languages use variables, operators, and literals in their expressions.

47. What do Angular lifecycle hooks do?

When developing an Angular application, there will be occasions when we need to run some code in response to a particular event, such as when a component is initialized, displayed, or removed from the screen. For instance, if a component includes an HTML element with an event listener attached, such as one for a button click or a form submission, we can remove the event listener before removing the component from the screen, just as we can fetch data and display it in a component after the component has been loaded on the screen.

48. Explain the bootstrap supported by Angular?

Both manual and automatic bootstrapping are supported by Angular. Let's quickly grasp the two.

• Manual bootstrapping: It provides experts more flexibility over how and when to initialize the Angular application. When professionals want to complete other jobs and processes before Angular generates the page, it is quite helpful.
• Automatic bootstrapping: If you need Angular to automatically bootstrap the application, automatic bootstrapping can be used to add the ng-app directive to the application's root, frequently on the tag. Once it locates the ng-app directive, Angular imports the related module and then builds the DOM.

Angular interview questions & answers at Advanced Level

49. What does RxJS's term "subscribing" mean?

When using observables in RxJS, we must subscribe to an observable in order to consume the data that passes through it. A subscriber uses this info that was produced by a publisher. When we subscribe to an observable, we pass in two functions—one for the data and one for errors—so that, in the event of an error, we can display a message or handle the message in some other way.

50. What is Angular CLI?

The angular command-line interface is another name for Angular CLI. Professionals may utilize Angular's CLI tools to add components, rapidly deploy them, carry out testing, and carry out many other tasks.

Those are the top angular interview questions & answers that will help professionals as well as freshers in getting through an interview and land a rewarding job position in any top company.

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