Angular Interview Questions

Most Asked Angular Interview Questions and Answers

1. What is data binding in Angular?

Data Binding is an important concept in Angular that helps in defining the communications between a web page component and a DOM. Data Binding is a process by which an internet user can manipulate the web page elements using a web browser. Mostly Data binding is used in web pages that contain interactive components like games, calculators, forms and tutorials. 

In simpler terms, Data binding keeps your web page up to date based on the state of your application. 

2. What is the difference between AngularJS and Angular?

We need to know that AngularJS and Angular are two different things. AngularJS uses Javascript whereas Angular uses Typescript language.  Coming to architecture, AngularJS supports model-view-controller design whereas Angular uses components and directives. 

One of the main points in favor of Angular is that AngularJS is not supported by mobile browsers whereas Angular is supported by all popular mobile browsers. Also, AngularJS is difficult to manage because of an increase in source code size, Angular is well structured, easier to create, and manages bigger applications. 

3. What are templates in Angular?

Angular templates allow you to define the UI of your applications. Angular-specific templates that are written in HTML contain Angular-specific elements and attributes. The prerequisites to learning template syntax is that you should be familiar with – HTML, CSS, and Javascript. 

With Angular syntax in your templates, you can extend the HTML vocabulary of the applications that you are building. One of the features is that Angular enables you to get and set DOM (Document Object Model ) values dynamically with features such as built-in template functions, variables, and data binding. 

4. What are directives in Angular?

Directives are attributes that allow the user to write new HTML syntax specific to the applications. These directives execute whenever the Angular compiler finds them in the DOM. Angular supports three types of built-in directives:

• Component Directives: These are the directives that come with a template and are the most common type of directives. 
   
• Attribute Directives: These are the directives that can change the appearance of a component, page or even other directives.
  
  The following command is used to create an attribute directive:

ng g directive YellowBackground 

We can manipulate the generated directive to look like - 

import { Directive, ElementRef } from '@angular/core';
      @Directive({
       selector: '[appYellowBackground]'
      })
      export class YellowBackgroundDirective {
       constructor(el:ElementRef) {
         el.nativeElement.style.backgroundColor = "yellow";
       }
      }

• Structural Directives – These directives are responsible for changing the DOM layout either by adding or by removing the DOM elements. Every structural directive has a ‘*’ sign before them.
  
  Example of built-in directives in action:
   

<div *ngIf="isReady" class="display_name">
          {{name}}
      </div>
      <div class="details" *ngFor="let y of details" >
          <p>{{y.name}}</p>
          <p> {{y.address}}</p>
          <p>{{y.age}}</p>
      </div>

*ngIf is used to check a boolean value and if it’s truthy,the div element will be displayed.

*ngFor is used to iterate over a list and display each item of the list

5. What are annotations in Angular? 

Annotations in Angular are used to create an annotations array. They are the metadata set on the class used to reflect the metadata library. 

Note that they are different from Decorators. Annotations and Decorators are two very different, competing and incompatible language features to compile the @symbols that we often see attached to the angular components. 

6. Explain the difference between one-way binding and two-way binding? 

One-way binding	Two-way binding
The view doesn’t change or update automatically whenever there is a change in the data model. Custom code needs to be manually written to reflect changes.	UI or view is continuously updated automatically as the data model changes. The process is similar to the synchronisation process.
One-way data binding will bind the data from the component to the view (DOM) or from view to the component.	Two-way data binding in Angular will help users to exchange data from the component to view and from view to the component. It will help users to establish communication bi-directionally.
One-way data binding is unidirectional. You can only bind the data from component to the view or from view to the component.	It will help users to establish communication bi-directionally.

7. Explain the bootstrapping module? 

Every application has at least one angular module, and the root module that we bootstrap to launch the application is actually called the bootstrapping module. It is also known as the AppModule. AngularCLI generates the bootstrapping module.

It has a default structure as shown below:

```javascript
/* JavaScript imports */
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';
import { AppComponent } from './app.component';

/* the AppModule class with the @NgModule decorator */
@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpClientModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

8. How can you perform error handling? 

If the request fails to reach the server or fails on the server, then in this case HTTPclient will return an error object instead of a successful response. To handle this issue, we need to pass the error object as the second callback to the subscribe() method.

fetchUser() {
  this.userService.getProfile()
    .subscribe(
      (data: User) => this.userProfile = { ...data }, // success path
      error => this.error = error // error path
    );
}

 

Also, it is always useful and a best practice to give the user some meaningful feedback instead of a raw error message that is returned by the HTTPclient. 

9. What is AOT? 

AOT stands for Ahead of time. It is a type of compilation that compiles your application at build time. For AOT compilation, we need to include the –aot option with the ng build or ng serve command. 

• ng build –aot
   
• ng serve –aot

10. What are the advantages of AOT? 

AOT has a lot of benefits as mentioned below:

• AOT helps in detecting and reporting the template binding errors earlier, that is during the build step itself.
  
  It also helps in providing faster rendering. The browser downloads a pre-compiled version of the application. So it can render the application immediately without compiling the app.
   
• AOT also inlines external HTML templates and CSS style sheets within the application javascript which eliminates separate ajax requests. Thus, it overall gives fewer asynchronous requests. 
   
• AOT does not need us to download angular compilers. Hence it helps in drastically reducing the application payload. 

Angular Interview Questions For Freshers

11. Can arrow functions be used in AOT? 

No, arrow functions cannot be used in AOT. Here is an example of a code snippet that is invalid:

@Component({
  providers: [{
    provide: MyService, useFactory: () => getService()
  }]
})

 

We can fix this as follows:

function getService(){
  return new MyService();
}


@Component({
  providers: [{
    provide: MyService, useFactory: getService
  }]
})

12. How can we inject dynamic script in Angular?

We can inject dynamic HTML, script, URL in angular by using DomSanitizer. 

import { Component, OnInit } from '@angular/core';
import { DomSanitizer } from '@angular/platform-browser';
@Component({
   selector: 'my-app',
   template: `
       <div [innerHtml]="htmlSnippet"></div>
   `,
})
export class App {
       constructor(protected sanitizer: DomSanitizer) {}
       htmlSnippet: string = this.sanitizer.bypassSecurityTrustScript("<script>safeCode()</script>");
   }

13. What are workspace APIs? 

Workspace APIs to make it easier for developers to read and modify the angular.json file instead of manually modifying it. We can enable or add optimisation build target as mentioned below:

import { NodeJsSyncHost } from '@angular-devkit/core/node';
import { workspaces } from '@angular-devkit/core';
async function addBuildTargetOption() {
    const host = workspaces.createWorkspaceHost(new NodeJsSyncHost());
    const workspace = await workspaces.readWorkspace('path/to/workspace/directory/', host);
    const project = workspace.projects.get('my-app');
    if (!project) {
      throw new Error('my-app does not exist');
    }
    const buildTarget = project.targets.get('build');
    if (!buildTarget) {
      throw new Error('build target does not exist');
    }
    buildTarget.options.optimization = true;
    await workspaces.writeWorkspace(workspace, host);
}
addBuildTargetOption();

14. Can you explain router imports? 

The Angular Router which represents a particular component view for a given URL is not part of Angular Core. It is available in a library named @angular/writer to import required router components. For example, we import them in-app module as below:

import { RouterModule, Routes } from ‘@angular/router’;

15. What are Macros? 

The AOT compiler supports macros in the form of functions or static methods that return an expression in a single return expression. 

Macros function- 

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

Macros can also be used inside metadata as an expression. 

@NgModule({
  declarations: wrapInArray(TypicalComponent)
})
export class TypicalModule {}

The compiler treats the macros expression as written directly. 

@NgModule({
  declarations: [TypicalComponent]
})
export class TypicalModule {}

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16. What is the difference between a component and a directive in Angular?

Components have a template associated with them that, in turn, describes the view that is rendered when a component is used. Any data or functions defined in a component are not accessible outside of that component.

On the other hand, Directives do not have a template by default. They can be used to manage the behavior and appearance of other elements on the page. 

17. Briefly explain the lifecycle hooks of an Angular component.

Angular components have several lifecycle hooks that allow developers to run code at different stages of the component's lifecycle. These hooks help in performing tasks like initialization, change detection, and cleanup. Some examples of lifecycle hooks are ngOnInit, ngOnChanges, ngOnDestroy, etc.

18. What do you understand about the concept of dependency injection in Angular?

Dependency injection is an important concept of Angular that allows developers to write concise, reusable code by separating the creation of objects from their use. It is a fundamental feature that is used to manage the dependencies between different components, services, and other objects in an application. The dependency injection system in Angular works by maintaining a hierarchical tree of injectors. Each injector is responsible for creating and managing a set of dependencies and can refer to parent injectors if a dependency cannot be resolved locally.

19. What is a service in Angular?

In Angular, a service is a type of class that is used to provide functionality that can be shared across multiple components, directives, and other services in an application. Services are used to encapsulate functionality that does not directly relate to the view layer, such as data access, network requests, or business logic. They also enable the reusability of code, improve application scalability, etc.

20. How can you have form validation in an Angular application?

In Angular, we can have form validation by using a combination of template-driven forms and reactive forms.

To add validation to a template-driven form, we can use built-in Angular directives such as 'required', 'minLength', and 'maxLength'. These directives work with the ngModel directive to validate user input and display error messages when needed.

To implement form validation with reactive forms, we define a validation function that checks the value of the form control and returns error messages if the validation fails. We can apply this validation function to the form control using the Validators class.

Angular Interview Questions for Advanced Level

21. Explain the concept of lazy loading in Angular?

Lazy loading is a feature in Angular that allows developers to load modules and components as per their demand on the action of a specific route rather than loading everything in advance. The feature helps improve the loading time, thereby increasing the application's performance.

22. What is the purpose of ngOnInit in Angular?

In Angular, ngOnInit is a lifecycle hook part of the Angular component lifecycle. The hook is invoked when a component is being initialized and is ready to perform any necessary setup tasks before being rendered. It NgOnInit is a method with no parameters and no return type.

23. Define scope in Angular.

Angular scope refers to the object that acts as a binding between the view (HTML) and the controller. It provides a method to share data and communicate between different components of an Angular application. It allows the controller to share properties with the view. Scope plays a crucial role in two-way data binding and dependency injection. It is also used to handle event propagation in Angular.

24. What do you understand about Angular Universal?

Angular Universal is a server-side rendering solution. It allows rendering the angular applications on the server before sending them to the client. The content of the application is available to first-time users instantly. This increases the performance and efficient search engine optimization, offering a better user experience.

25. Mention some differences between Angular and React?

The key differences between React and Angular are:

React	Angular
React is a javascript library.	Angular is a complete framework
React can be used with either javascript or typescript.	Angular is mainly written in typescript.
React uses one-way data binding	Angular uses two-way data binding.

26. What is a module in Angular?

In Angular, a module is like a package that is used to organize and bundle related components, directives, services, and other features of an application. It helps manage dependencies and creates a self-contained unit of functionality that can be easily reused in different parts of the application. The @NgModule decorator is used to define every module in Angular.

27. What are template-driven and reactive forms in Angular?

Template-driven forms depend mostly on the directives in the HTML template. The validation details in the form are stated within the template itself with the help of NgForm, NgSubmit, and NgModel directives. Template-driven forms are suitable for simple forms.

Reactive forms, on the other hand, come with more advanced features. They are based on reactive programming principles. Reactive forms allow the users to define and control form elements and their behavior directly in the component code. Classes like FormControl, FormGroup, and FormArray from Angular's ReactiveFormsModule module are used to create and manage these form controls programmatically.

28. What are Angular pipes? Mention some examples of built-in Angular pipes.

Angular pipes are a feature in Angular that enables data transformation and formatting in Angular templates. Pipes take in an input value and transform it into a required output format. Some built-in examples of pipes in Angular are:

• DatePipe to format dates, 
• CurrencyPipe to format currency values based on the given currency code, 
• UpperCasePipe and LowerCasePipe convert text to uppercase or lowercase, etc.

29. What are impure pipes in Angular?

In Angular, pipes are used to transform data in Angular templates. By default, pipes are "pure," which means they are only called when the input values they depend on change. However, we can make a pipe "impure" by setting the pure property to false. This means the pipe will be called in every change detection cycle, regardless of whether the input values have changed or not. 

30. What is the use of NgRx in Angular?

NgRx is a state management library in Angular that is based on Redux. NgRx helps in managing the state by separating it from the components, thus implementing a unidirectional data flow. It combines all events and defines a common state in the angular application.

31. How to handle HTTP requests in Angular?

In Angular, we use the HttpClientModule to handle the operations related to HTTP requests. First, we need to import the module into the component. To make requests to the server, we can use the get(), put(), post(), and delete() methods of the HttpClientModule. To receive the response, we need to subscribe to the response using the subscribe() method. The HttpClientModule provides a simplified API to make HTTP requests.

32. Explain the HTTPClientModule.

In Angular, the HttpClientModule is a built-in module that helps in making HTTP requests to remote servers or APIs. It is part of the @angular/common/http package and is used for handling asynchronous HTTP requests and responses. The HttpClientModule provides the HttpClient service, which is used to make HTTP requests. It supports various HTTP methods such as GET, POST, PUT, DELETE, etc.

33. What do you understand by RxJs in Angular?

RxJs, or Reactive extensions for JavaScript, is a fundamental library in Angular that supports reactive programming with the help of observables. It handles asynchronous operations, callbacks, event handling, and data flow management.

34. How to optimize an Angular application to increase its performance?

There can be various methods by which we can increase the performance of an Angular application. They are:

• Reducing the bundle size 
• Lazy loading to load only the necessary code when required 
• AOT Compilation to pre-compile templates and reduce the runtime overhead
• Reactive programming to minimize unnecessary API calls and optimize data flow.

35. Differentiate between Angular Expressions and Javascript Expressions?

Angular expressions are a subset of JavaScript expressions. While Angular expressions are used inside Angular templates to bind data and dynamically display values, Javascript expressions are used in programming to perform calculations, build logic, and manipulate data. Unlike Javascript expressions, we cannot have conditionals and loops in Angular expressions. Angular expressions are evaluated by Angular's templating engine when the rendering process occurs, whereas the JavaScript engine executes JavaScript expressions at runtime.

Angular Interview Questions for Experienced

36. What are Angular guards?

Guards are a feature in Angular that allows users to manage and control the application's routing. Angular Guards can protect routes, control access to certain routes based on user authentication, and perform pre-navigation checks or modifications.

37. Briefly explain the working of Angular interceptors.

Angular interceptors provide a way to intercept and modify HTTP requests and responses globally in an Angular application. Interceptors are implemented as classes that implement the HttpInterceptor interface. When an HTTP request is made, the interceptors in Angular are executed in a chain before the request reaches the server. 

Similarly, when receiving an HTTP response, the interceptors are executed in a chain before the response reaches the calling code. 

38. How can you interact between the components of Angular?

In Angular, we can interact between the components using various techniques. We can either use input properties to pass data from parent to child component or use the output properties with event emitters to emit events from a child to its parent component. We can also use the RxJs observables to establish a connection between the components and share data.

39. What is the purpose of decorators in Angular?

Decorators are used in Angular to add metadata and configuration to Angular elements like components, services, directives, pipes, etc., that state how these elements will be processed and constructed.

There are four different types of decorators in Angular:

Method decorator: This decorator is applied to a method within a class and allows you to modify or enhance the behavior of that method. It can be used to add functionality around the method execution.

Class decorator: This decorator is used to enhance the behavior of a class.

Parameter decorator: This decorator is added to the parameters of a method.

Property decorator: This decorator is applied to a particular property and can modify accessors, define bindings, or perform validation.

40. Differentiate between AOT and JIT in Angular?

AOT and JIT are two modes of compilation in Angular. The differences between AOT and JIT are as follows.

AOT	JIT
AOT stands for Ahead of Time.	JIT stands for Just in Time.
It is a process where Angular templates and components are compiled during the building phase.	It is a process where Angular templates and components are compiled in the browser at the time of execution.
AOT compiles the templates into efficient JavaScript code that can be executed directly by the web browser without the need for further compilation at runtime.	JIT compilation generates the JavaScript code for templates as the application runs, which leads to a small delay during application startup.

41. What do you understand about the concept of view encapsulation in Angular?

View encapsulation in Angular refers to how styles and templates are confined to a particular component's view. It ensures that the styles and templates defined within a component do not affect other components in the application. There are three types of view encapsulation in Angular:

Emulated: In an emulated view, the styles defined within a component are encapsulated within that component's view and do not affect other components.

Native: Native view encapsulation in Angular uses the browser's built-in Shadow DOM technology to isolate component styles and templates. This ensures they do not affect or get affected by other components.

None: With the none view encapsulation, styles defined in a component can affect the entire application.

42. Explain the Angular decorators @Input and @Output.

The Angular decorators are used to connect components and interchange data between them. While the @Input decorator allows users to pass data from a parent component to a child component, the @Output decorator allows a child component to emit/trigger events and send data back to the parent component. The @Input and @Output component facilitates sharing and modification of data between the components.

43. Explain the ngClass directive in Angular.

The ngClass directive in Angular is used to apply CSS classes to an HTML element based on certain expressions or conditions. It allows developers to dynamically add or remove CSS classes based on the values of properties in your component. This directive is useful in highlighting, controlling the visibility, or applying different styles based on component properties or user interactions.

44. What is the purpose of ngStyle in Angular?

The ngStyle directive in Angular is used to apply inline CSS styles to HTML elements dynamically based on specific conditions. It allows users to modify and control the styling of elements with different colors, sizes, fonts, etc., within the component template of the angular application. Thus we have an interactive and responsive UI with the help of the ngClass directive.

45. How can you have responsive web designs in Angular?

We can use CSS media queries to have responsive web designs in Angular. The ngClass and ngStyle directive can be used to apply conditional styling to the HTML elements. Additionally, the BreakpointObserver service in Angular comes with predefined breakpoints and can be used to adjust the layout and style of the application based on different screen sizes without actually writing the CSS media queries. 

46. Explain transpiring in Angular.

In Angular, transpiring refers to the process of converting the TypeScript code into JavaScript code that can be understood and executed by web browsers or other JavaScript runtime environments. Transpiling in Angular occurs internally as a part of the build process.

47. How can you improve the size of Angular bundles?

Improving the size of Angular bundles can significantly increase the performance of the Angular application. This can be achieved by:

• Code minification: reducing the size of the code by removing unnecessary parts.
• Tree shaking: to remove unused code from the bundles
• Lazy loading: loading components and modules on-demand
• Optimizing dependencies, etc.

48. How can you add SASS to your Angular project?

We can use the Angular CLI to add SASS to our Angular project from the beginning. To do so, we can use the ng new command with the --style=sass option. This sets SASS as the default style preprocessor for your project, and all components will be generated with preset SASS files.

Example:

ng new <Project_Name> --style = sass

If the project has already been created and you want to switch to SASS, you can use the ng set command to change the default style extension to .scss (SASS).

Example:

ng set defaults.styleExt scss

49. What is the purpose of decorators @ViewChild?

The purpose of the @ViewChild decorator in Angular is to obtain a reference to a particular child component or element within a parent component. It allows users to access the properties, methods, and events of the selected child component or element directly from the parent component. This decorator is useful when we need to interact with a specific child component or element, such as accessing its data, calling its methods, etc.

50. When do you use the @ContentChild decorator?

The @ContentChild decorator in Angular is used when we want to access the first occurrence of a directive or component within the content of a component. It allows users to get a reference of a specific element or component that is projected into the component's view. Thus @ContentChild provides a method to identify and work with the projected content in a more controlled way.

Frequently Asked Questions 

Q. How do I prepare for an Angular Interview?

From an interview preparation point of view, firstly, clear all the basic concepts of the Angular framework. Many questions asked in the interview test your basic understanding of the framework. Second, Practice! Don’t just go through the theory but apply the angular framework in your applications. The more you use it, the better you will understand its concepts and various uses. 

Third, go through the Angular Interview Questions on the framework by the company that you are interviewing for.

Q. How do I interview a senior Angular Developer?

You can ask specific questions about the features of Angular and its core concepts. Then, you can ask the candidate about the real-world project experience he/she has. Furthermore, test the candidate with some problem-solving questions and his/her experience with testing Angular applications.

Q. What is the test for Angular Developer?

The test for Angular Developer should consist of angular concepts, coding problems, code reviewing and optimization of codes, real-world project experience, debugging exercises, and questions judging the familiarity with Angular CLI and integration with backend APIs.

Q. What is data binding in Angular interview questions?

Data binding in Angular is a way for your HTML to display data from your TypeScript code. It keeps your web page updated in real-time as your data changes, making sure what users see is always current.

Q. What is module in Angular interview questions?

In Angular, a module is like a container that groups related things like components, services, and directives. It helps organize your app and makes it easier to manage, especially as it grows bigger.

Conclusion

Angular is a fun framework and you can have so much fun and discover so many new things while working on this. We understand that preparing for interviews can be nerve-wracking and hope these Angular Interview Questions will help you during your interviews and you learn and grow in your role!  

These were some of the most commonly and frequently asked conceptual Angular Interview Questions that every candidate must know before going to sit in an interview. So how many of these questions did you already knew? Doesn’t matter, what matters is that now you know them and will be able to answer and explain the concepts fluently to the interviewer! 

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You can also consider our Interview Preparation Course to give your career an edge over others.