One of the most well-liked JavaScript frameworks for single-page applications is Angular. Also, it is very big and challenging to navigate. It is quite difficult to determine which components of the Angular framework you should become familiar with, making it even harder to find answers to Angular interview questions. As a result, we have created a collection of the most often asked Angular interview questions and answers.
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Top 100 Angular Interview Questions and Answers 2024
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, routing, layout, forms, reactivity, validation, etc.
2. What are the technologies used in Angular?
Google created the cutting-edge JavaScript frontend framework known as Angular. For several reasons, including to make certain activities 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. Each legitimate JavaScript is thus a legitimate TypeScript. Yet, 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.
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3. Why were client-side frameworks like Angular introduced?
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. Often, 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. Since then, even mobile phones have enough capacity 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.
4. How does an Angular application work?
The components of Angular are what make it function. Hence, 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. The material from the component is displayed once it has been loaded.
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5. What is TypeScript?
The majority of front-end developers prefer the TypeScript capability that Angular offers. By automatically filling, TypeScript makes efficient error detection and simple compilation possible. Moreover, it provides robust interfaces, access restrictions, hybrid kinds, etc. When combined, all of these result in a shorter development period.
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
7. What is metadata?
We instruct Angular on how to handle a class by using metadata. Until 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. What is the difference between constructor and ngOnInit?
| 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?
In order to instruct Angular how to handle a class, we need metadata. A component behaves as a class when it is used unless we explicitly inform Angular that it is a component, which we accomplish with the aid of metadata. With a decorator, TypeScript attaches metadata. Decorators are functions that are knowledgeable about class settings and intended behavior.
10. What is the purpose of the async pipe?
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. Currently, 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 is the option to choose between inline and external template?
Inline templates are typically utilized for short codes and external templates for somewhat large displays. Nonetheless, company policy, conditions, etc., sometimes determine whether to use inline or external templates.
12. What is the purpose of ngFor directive?
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.
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13. What is 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 happens if you use script tag inside 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. What are 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. What are template statements?
Template statements in Angular refer to the operations or elements that are used in HTML in response to user events. By activities like the presentation of dynamic content or the submission of forms, among others, these template statements enable your application to engage users.
17. What is the difference 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?
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. Moreover, 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. 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.
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The various types of 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?
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 bootstrap custom elements?
The answer is no, you don’t need to bootstrap custom elements because they do so when they are added to the DOM. Moreover, Angular’s custom elements are automatically destroyed when they are 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’s break down 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.
DOM modification to include the custom element: Similar to how built-in HTML is added to the DOM, the custom element is.
Browser creates a class based on a component: An instance of the registered class is produced by the browser and added to the DOM once the custom element has been introduced.
Data binding and change detection are enabled in the last stage by the newly created instance. The component and DOM data are used to render the template’s content.
25. How to transfer components to custom elements?
Transferring components to custom elements requires two crucial procedures to be taken:
Building 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. Via this conversion, the NgElementConstructor interface is implemented, resulting in a constructor class that can be used to produce a self-bootstrapping instance.
element class registration with the browser The configured constructor and the corresponding custom-element tag are registered with the browser’s CustomElementRegistry using the customElements.define() function.
26. What are the mapping rules between Angular component and custom element?
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.
T
The outputs from components are sent as HTML Custom Events with names that are identical to the output names.
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?
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.
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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?
Error handling in Angular may be accomplished by creating a function that uses RxJS’s catchError and HttpClient’s catchError. The HttpClient in Angular parses JSON replies and returns a JavaScript object in the observable to handle problems.
35. What is content projection?
The term “Content projection” in the context of Angular refers to a pattern where you can project the material you wish to use within another component. Consider a Card component, for instance, which may accept content from 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?
One of the most significant and potent aspects that aid in creating communication between the DOM and the component is data binding. As 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.
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 utilizing Angular has a lot of advantages, there are some drawbacks as well. These are what they are:
In 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.
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39. What do you mean by string interpolation?
The mustache 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 expressions that Angular must run to acquire the result are included within the brackets and can then be put into the HTML code. Also, these expressions are consistently updated and saved as part of the digest cycle.
40. What are the differences between Angular decorator and 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.
41. What is an AOT compilation in Angular?
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.
42. What are the advantages of AOT?
AOT compilation has several advantages as mentioned below:
Fast rendering:Â 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?
The fundamental unit of the Angular user interface is the component. A component for a particular area of a user interface is made up of HTML, CSS, and JavaScript. They 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.
45. What are dynamic components?
The Angular framework’s Dynamic Components are the components that make it simple to create complex applications. Typically, runtime is when dynamic components are instantiated and added to the application.
46. What is the purpose of base href tag?
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 files during navigation by the Angular router.
47. What are modules in Angular?
A logical boundary of our 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, and our application would still function as intended. With the NgModule decorator, we build a module in Angular.
48. What is DOM?
Document Object Model, or DOM in its full name, 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.
49. What are services in Angular?
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.
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 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. Lifecycle hooks are employed for this purpose. 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.
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52. What are templates?
Angular-specific elements and attributes are used in the HTML used to create Angular templates. The user can be presented with a dynamic view by combining the templates with data from the controller and model, which can then be rendered.
53. What is a two-way data binding?
In order to guarantee that the data model and the view are automatically synced, Angular uses two-way data binding. For instance, when a user modifies some data in a model that is presented in numerous locations throughout a component, the update should be updated everywhere.
Since a very long time ago, Angular has enabled two-way data binding. It should, however, be utilized with caution because it may result in subpar application performance or performance deterioration over time. The term “two-way data binding” refers to the ability to alter some component model data from an HTML view and have that change propagate to all other locations in the view where it is displayed.
54. What are pipes in Angular?
Sometimes, before putting the data into our templates, we may need to change or transform it in order to output some dynamic data. Although there are a few ways to accomplish that, using pipes in Angular is the most popular one. A pipe is only a basic function that we can employ in our templates’ expressions.
Pipes are quite helpful because they only need to be declared once and registered with the Angular framework before we can utilize them across our application. UpperCasePipe, LowerCasePipe, CurrencyPipe, and other popular built-in pipes in Angular are just a few examples.
55. What are observables in Angular?
With an observer, we may conduct asynchronous activities declaratively. Observables are conceptualized as data streams that are transmitted from a publisher to a subscriber. Because they both deal with responding to asynchronous requests, they are comparable to promises. Observables are thought to be a better alternative to promises, though, as the former has many operators that enable developers to handle asynchronous requests more effectively, particularly if there are multiple requests coming in at once.
Many developers choose observables because they give them the ability to conduct a variety of actions, including the ability to combine two observables, map one observable into another, and even pipe numerous operations through an observable to change its data.
56. How are observables different from promises?
Although promises and observables are both used in JavaScript to manage asynchronous requests, they function substantially differently. While observables may manage a series of asynchronous events over time, promises can only handle a single event at a time. Moreover, observables give us access to a wide range of operators that make it simple for us to alter data that is passing through them.
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, as opposed to simply wrapping asynchronous operations in a promise to make them more usable.
57. What does Angular Material mean?
Professionals may create consistent, beautiful, and fully functional websites, web pages, and web applications using the UI component framework Angular Material. By adhering to contemporary web design ideas like browser probability and gentle degradation, it is made capable of doing so.
58. What is RxJS?
The name RxJS means for Reactive Extensions for JavaScript, and it refers to a library. It is utilized so that we may implement reactive programming in our JavaScript project by using observables. Because it enables us to combine our callback-based or asynchronous code into a sequence of operations executed on a stream of data that emits values from a publisher to a subscriber, RxJS is utilized in several well-known frameworks, including Angular. Libraries exist for Java, Python, and other languages that enable the creation of reactive programming utilizing observables.
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.
60. What do you mean by dependency injection?
A software design pattern called dependency injection (DI) in Angular allows objects to be supplied in the form of dependencies as opposed to having them hard-coded in the appropriate components. When it comes to dividing the development of object logic from its use, this idea is really useful.
In order to load the module and obtain the application parts, the function “config” requires DI, which needs to be configured. Furthermore, this capability enables experts to modify dependencies in accordance with requirements.
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61. What are Angular building blocks?
- 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:Â 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:Â 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.
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63. Describe Angular authentication and authorization.
A user’s login information is provided to a server-based authenticate API. The server returns a JSON web token (JWT), which contains the current user’s properties and data, after validating the credentials. Moreover, JWT makes it simple to identify the user; this procedure is known as authentication.
Users have different sorts and levels of access after logging in; some may have unrestricted access to all resources, while others may. The level of access for these users is determined by authorization.
64. What is the digest cycle process in Angular?
In an Angular process called a digest cycle, the watch list is tracked to keep tabs on changes in the value of the watch variable. The current and prior versions of the scope model values are compared during each digest cycle.
65. What are the distinct types of Angular filters?
As a component of Angular, filters assist in formatting the expression value before it is displayed to the user. Services, directives, templates, and controllers can all add them. Also, you have the choice to design custom filters based on your needs. With the help of these filters, you can quickly organize the data so that only the information that satisfies the required criteria is shown. 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
67. What does subscribing mean in RxJS?
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.
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68. What is Angular Router?
Responding to changes in the URL brought about by adding and removing content from the application is the work of routing in a single-page frontend application. This is a challenging assignment because we don’t want the browser to refresh, therefore we must first intercept a request that modifies the browser’s Address. Then, we must choose which material to add and which to delete, and finally, we must modify the URL of the browser so that it displays the user’s current page.
As we can see, putting this into practice may be rather challenging, especially when using it in several applications. Because of this, Angular has a comprehensive routing solution for single-page applications.
69. What is REST?
Representational State Transfer is known as REST in Angular. It is an API that responds to HTTP requests. Here, the requested URL leads to the data that needs to be processed, and an HTTP function is then utilized to determine which operation must be carried out on the provided data. RESTful APIs are the name given to the APIs that use this approach.
70. What is the scope?
In Angular, a scope is an object that alludes to the application model. It is a setting in which expressions can be used. These scopes are arranged in a hierarchical manner that resembles the DOM structure of the application. A scope aids in watching expressions and spreading various occurrences.
71. Explain Angular CLI.
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.
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?
Complex logic is made possible through schematics, which are template-based code generators. It is often installed using npm and packed into collections. Schematics are used to generate or alter codes in order to change a software project.
74. What is a rule in Schematics?
In Schematic, the term “Rule” refers to a set function that takes a Tree, modifies it, and then outputs a fresh Tree.
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75. What is Schematics CLI?
Schematics CLI is used to transform web-based applications projects.
76. What is HttpClient, and what are its benefits?
An Angular module called HttpClient is used to interact with a backend service via the HTTP protocol. We typically utilize the fetch API in frontend applications to send requests. The fetch API, however, makes use of promises. Although promises are helpful, they lack the extensive functionality that observables provide. Due to the fact that HttpClient returns the data as an observable that we can subscribe to, unsubscribe from, and perform a number of actions on using operators, we use it in Angular. Both promises and observables can be formed from one another. Promises can be converted into observables.
77. What is multicasting in Angular?
The HttpClient module in Angular allows us to interface with a backend service and retrieve data. Once the data has been retrieved, we can broadcast it to numerous subscribers in a single execution. Multicasting is the process of reacting with data to numerous subscribers. That is very helpful when several components of our apps are awaiting data. We must utilize a RxJS topic in order to use multicasting. Observables do not support multiple subscribers because they are unicast. Subjects do, however, support many subscribers and are multicast.
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78. What is a directive in Angular?
Angular comes with a large number of directives. To ensure that the compiler is aware of them and uses them during the compilation stage, we can build our directives and communicate their functions to Angular.
79. What will happen if you do not supply handler for observer?
The observer automatically ignores notifications of that type when a handler is not provided for them, and the observer instance only publishes value when it is subscribed to.
80. What are angular elements?
Angular components, which are a web standard for defining new HTML elements and are bundled as custom elements, are referred to as angular elements. Web Components is another name for these unique pieces. When added to the DOM tree, the Angular custom elements bootstrap themselves automatically.
81. What is the browser support of Angular Elements?
Angular elements are supported by Chrome, Edge (Chromium-based), Firefox, Opera, Safari, and other modern browsers via polyfills because Angular is built on the most recent web platform standards. Whole Angular applications can run thanks to polyfills.
82. What is the role of SPA in Angular?
The term “single page application” is SPA. Even though the URL is continually changing, our technique just keeps index.HTML, one page, up to date. Compared to conventional web technology, SPA technology is simple to develop and incredibly quick.
83. 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:Â 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.
84. 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.
85. What is the purpose of the common module in Angular?
The common module in Angular is a module that contains all the frequently used elements of Angular, such as services, pipes, directives, etc. It is available under the package @angualr/common. Also, it contains a few sub-modules, including the HttpClientModule from the @angular/common/http package. Due to Angular’s modular design, its functionalities are kept in manageable, self-contained modules that can be imported and added to our projects as needed.
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86. What are the differences between AngularJS and Angular?
- 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.
87. What are the differences between Angular expressions and JavaScript expressions?
JavaScript expressions and Angular expressions are very different from one another since Angular allows us to write JavaScript in HTML, but plain JavaScript does not. Moreover, all Angular expressions are localized. Nevertheless, these expressions in JavaScript are only applicable to the global window object. But when the Angular compiler takes the Angular code we’ve written and turns it into normal JavaScript, which a web browser can subsequently understand and utilize, these discrepancies are resolved.
88. What is server-side rendering in Angular?
In a typical Angular application, JavaScript manages all user interactions while the browser runs our application. Due to this, our page’s load time can occasionally be significantly slowed down if we have a huge application with a high bundle size since it must download all the necessary files, parse the JavaScript, and then execute it. We can utilize server-side rendering to get around this delay, which enables us to deliver a completely rendered page from the server that the browser can display and then let the JavaScript code handle any further user interactions.
89. 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.
90. What is the difference between interpolated content and the content assigned to the innerHTML property of a DOM element?
When we enter a JavaScript expression inside double curly braces, such as “someExpression(),” Angular interpolation takes place. Using this, dynamic content can be added to a web page. Alternatively, we may achieve the same result by supplying some dynamic content to a DOM element’s innerHTML attribute. The difference between the two is that in Angular, the compiler always escapes the interpolated content, preventing HTML from being interpreted, and the browser instead shows the code as it is with brackets and symbols rather than the output of the interpreted HTML. In contrast, innerHTML interprets the content as HTML code if it is HTML.
91. What are HttpInterceptors in Angular?
HttpInterceptors are used to analyze and transform HTTP requests as well as HTTP responses. They are a component of the @angular/common/HTTP module. These interceptors are designed to carry out checks on a request, alter the answer, and carry out cross-cutting tasks like logging requests, user authentication via requests, response compression using gzip, etc. You should now have a better understanding of Angular as a framework, as well as its numerous features and functionalities, thanks to these Angular interview questions for 2021. You may better grasp the types of interview questions by reading through these frequently asked questions, which will also help you understand Angular interviews and Angular as a framework.
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92. 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
93. What is ng-content and its purpose?
In Angular, ng-content is used to dynamically insert material inside the component. It aids in passing content inside the component selector and enhancing component reuse.
94. 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.
95. What is folding?
When Angular generates the code, it’s possible that some of the non-exported members get folded. This procedure, known as folding, in which the collector evaluates an expression and records the outcome in the.metadata.json file, is known as folding.
96. 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];
}
97. 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
98. 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
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99. 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
});
});
}
}
100. What is NoopZone?
NoopZone aids Angular in determining and understanding when to initiate the change detection. But, the NoopZone also has to be defined if Angular is to be used without a zone.
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