Top Angular 8 Interview Questions for 2023 - IQCode

Overview of Angular 8

Angular is a widely used open-source web application framework led by a team at Google, as well as a community of individuals and corporations. It is built on TypeScript, a superset of JavaScript, and is known for being the frontend of the MEAN stack which includes MongoDB, Express.js, Node.js along with Angular.

Angular 8 is a TypeScript-based client-side framework used for creating dynamic web applications. It has extensive features, making it very similar to its previous versions but with significant differences. Due to its popularity, Angular 8 is highly in demand in the software industry, and many top companies use Angular 8 for developing web applications.

In this article, we’ll delve into common interview questions about Angular 8 that cover both basic and advanced topics.

Basic Interview Questions on Angular 8

  1. What are some features of Angular 8 that differentiate it from previous versions?

Understanding Ivy in Angular 8

In Angular 8, Ivy is the new rendering engine that replaces the View Engine used in previous versions. Ivy provides several benefits to developers such as smaller bundle sizes, improved debugging, and better template type checking.

One of the major features of Ivy is that it enables Angular to generate less code, leading to smaller bundle sizes. This is achieved through features like Ahead-of-Time (AOT) compilation, tree-shaking, and lazy loading. As a result, end-users get faster load times for their applications.

Another advantage of Ivy is that it simplifies the process of component creation and improves template type checking. Ivy produces more efficient and optimized component code for developers, thus making it easier to build high-performance apps.

Lastly, Ivy also offers improved debugging tools, which makes it easier for developers to find and fix issues in their code. Ivy’s improved Error messages help developers identify exactly where and what caused an error to occur in their application.

Overall, Ivy is a significant improvement in Angular 8 and provides developers with better performance, improved developer experience, and better debugging capabilities.

What is the purpose of using Bazel in Angular 8?

Bazel is a build tool that is used for automating the build and deployment process of software applications. In the context of Angular 8, Bazel is used to build, test, and package an Angular application for deployment. It helps with the efficient management of dependencies and makes development and testing processes much faster and scalable. The use of Bazel in Angular 8 also enables developers to build optimized and optimized bundles for production builds. Overall, Bazel is a powerful tool that is especially beneficial for large-scale Angular projects that have complex and diverse dependencies.

What is Codelyzer in Angular 8?

Codelyzer is a linter tool for Angular that helps maintain consistency and standards in coding. It is essentially a set of rules and recommendations designed to enforce best practices and make it easier to write clean and maintainable code. By using Codelyzer, developers can catch errors and potential issues early on in the development process, which reduces the need for debugging and improves the overall quality of the application. Codelyzer can be installed easily through npm and integrated into an Angular project.

The Importance of Wildcard Route in Angular 8

In Angular 8, a wildcard route is a fallback route that is used when there is no other route available to match the current URL. This route is denoted by the '**' symbol and is defined at the end of the route definition.

The importance of wildcard route lies in its ability to handle any URL request that does not match any of the other configured routes. Without it, Angular would return a 404 error for any such request.

Wildcard routes also provide flexibility in the application's navigation structure by allowing for dynamic URL parameters to be passed as part of the request. This can be especially useful for complex applications with nested components and child routes, allowing for multiple levels of navigation and dynamic content loading.

In summary, using wildcard route in Angular 8 is an important technique to ensure that your application can gracefully handle requests for undefined or non-existent routes, and to provide flexible navigation options for your users.

Reasons for using Reactive Forms in Angular 8

Reactive Forms in Angular 8 are used for several reasons, including:

  1. Ability to handle complex forms with advanced validation requirements
  2. More control over form data with observable real-time updates
  3. Better testing capabilities with isolated unit tests
  4. Easier programmatically generating forms
  5. Improved performance compared to Template-driven forms

In summary, Reactive Forms in Angular 8 provide developers with a powerful toolset for creating interactive and responsive forms, making it a popular choice for building complex web applications.

Reasons for using Template-Driven Forms in Angular 8

Template-Driven Forms are used in Angular 8 for several reasons, such as:

- They are easier to use and understand for simple forms that don't require complex validation and logic.

- They enable automatic two-way binding between the form and the component, simplifying data management.

- They provide built-in directives and services that handle common form tasks like validation, error messaging, and form submission.

- They have a lower learning curve compared to Reactive Forms, making it easier for developers who are new to Angular.

- They can be used with minimal changes to existing HTML forms, allowing for faster development and easier maintenance.

Overall, Template-Driven Forms are a great choice for simple forms that don't require advanced customization or complex validation logic. However, if a form requires more advanced features or complex logic, Reactive Forms may be a better option.

Checking the Type of a Variable in Angular 8

In Angular 8, we can use the typeof operator to check the type of a variable. The typeof operator returns a string that represents the data type of the variable.

For example, if we have a variable named "num" and we want to check its type, we can use the following code:

let num = 10;
console.log(typeof num); // Output: "number"

This code will output "number" because we assigned the value 10 to the variable "num" and 10 is a number.

Similarly, if we have a variable named "str" and we want to check its type, we can use the following code:

let str = "Hello World";
console.log(typeof str); // Output: "string"

This code will output "string" because we assigned the value "Hello World" to the variable "str" and "Hello World" is a string.

Using the typeof operator is a simple and convenient way to check the type of a variable in Angular 8.

How to Load and Run an Angular Application

To load and run an Angular application, follow these steps:

1. Install Node.js and npm. 2. Install the Angular CLI globally using the command `npm install -g @angular/cli`. 3. Create a new Angular project using the command `ng new project-name`. 4. Navigate to the project directory using the command `cd project-name`. 5. Run the server using the command `ng serve`. 6. Open a web browser and navigate to `http://localhost:4200/` to view the application.

Make sure to regularly update your dependencies and follow best practices for efficient and effective development.

Angular 8 Architecture: Key Components

In Angular 8, the architecture can be divided into the following key components:

- Modules: Angular applications are divided into separate modules, each serving a specific functionality. This makes the code organized and reusable.

- Components: Components represent the UI building blocks of the application. Each component has its own set of logic, styles, and templates.

- Templates: Templates are used to define how a component should be rendered.

- Forms: Angular provides a set of APIs to handle forms and user input.

- Services: Services are used to share data, logic, and functionality across multiple components.

- Dependency Injection: Angular has a powerful dependency injection system that makes it easy to manage dependencies and make components more modular.

- Routing: Angular's built-in router helps to manage navigation and routing within the application.

- Directives: Directives are used to add behavior to elements in the DOM. Angular comes with built-in directives, as well as the ability to create custom ones.

- Pipes: Pipes are used to transform data before it is displayed in the UI.

- RxJS: RxJS is a powerful library for handling asynchronous programming in Angular. It provides a set of APIs for observables, which make it easy to manage streams of data in real-time.

Understanding these key components is essential for building scalable and maintainable Angular applications.

Lazy Loading in Angular

Lazy Loading is a design pattern used in Angular to load only the necessary modules or components when users navigate to particular routes or perform specific actions, avoiding unnecessary loading time for the entire application. It helps improve the performance of the application by splitting it into smaller chunks and loading them on-demand. Here's how to use Lazy Loading in Angular:

  const routes: Routes = [
    { path: '', redirectTo: '/home', pathMatch: 'full' },
    { path: 'home', component: HomeComponent },
    { path: 'lazy', loadChildren: './lazy/lazy.module#LazyModule' }

In the above code, we have a route defined for the HomeComponent and a lazy-loaded module LazyModule. When users navigate to the '/lazy' route, Angular will only load the LazyModule and its components instead of the entire application.

To achieve Lazy Loading in Angular, we need to use the loadChildren property in route configuration, which specifies the path to the lazy module along with the module file name followed by '#'. This tells Angular to load the module lazily when the route is activated.

Creating an Angular Application in version 8

To create an Angular application using version 8, follow these steps:

1. Make sure you have Node.js and npm installed on your machine. You can install them from the official Node website.

2. Open your terminal or command prompt and execute the following command to install the Angular CLI globally:

npm install -g @angular/cli@8

3. Once the installation is complete, create a new Angular project with the following command:

ng new project-name

This command will generate a new project with all the necessary files and dependencies installed.

4. Navigate into the project directory using:

cd project-name

5. Finally, start the development server with the following command:

ng serve

This will launch the development server and serve your application on


You're now ready to start building your Angular application in version 8!

What is the use of ngUpgrade in Angular 8?

The ngUpgrade module in Angular 8 allows developers to simultaneously run and migrate AngularJS (Angular 1.x) applications to Angular. This module provides a set of utilities that assist in AngularJS to Angular migration while allowing developers to use both libraries in the same project. The migration process can be done one component at a time, without the need for a complete rewrite of the application. This helps to save time and effort while upgrading an older AngularJS application to the latest version of Angular.

Syntax and Use of the NgIf Directive in Angular

The syntax for the NgIf directive in Angular is as follows:

<div *ngIf="condition">Content to show when condition is true</div>

The `*` syntax is used to indicate that the directive is a structural directive, which means it can add or remove elements from the DOM.

The `ngIf` directive is used to conditionally render elements based on a given expression. If the expression evaluates to true, the element is displayed. If it evaluates to false, the element is removed from the DOM. This can be useful for showing or hiding elements based on user input or other state changes in the application.

For example, you could use the NgIf directive to show a loading spinner while waiting for data to load from a server, and then display the data once it is available.

Concept of Data Binding

Data binding is a technique that establishes a connection or a link between the user interface (UI) and the data source of an application. In simpler terms, it synchronizes the data between the model and the view of an application.

In data binding, any changes made to the UI are also reflected in the data source and vice versa. This eliminates the need for extra code to update the views or models.

Data binding can be done in two ways:

1. One-way data binding: Data flows from the data source to the view or vice versa, but not both. 2. Two-way data binding: Data flows both ways, i.e., from the data source to the view and from the view to the data source.

Data binding improves the efficiency of an application’s code and reduces the amount of code needed to manage data. It is a popular technique used in many modern web frameworks and is an essential concept for developers to understand.

Explanation of String Interpolation in Angular 8 with an Example

String interpolation is a feature in Angular 8 that allows values of TypeScript expressions to be displayed as a string. It is done by using double curly braces {{}} in the component's template. When an expression is placed within the curly braces, it is evaluated and its value is displayed as a string.

For example, consider the following component:

import { Component } from '@angular/core';

 selector: 'app-example',
 templateUrl: './example.component.html',
 styleUrls: ['./example.component.css']

export class ExampleComponent {
 name = 'John Smith';
 age = 25;

In the template of the component, we can use string interpolation to display the values of the name and age properties defined in the component:

<h4>My name is {{name}} and I am {{age}} years old.</h4>

When this component is rendered, it will display the following text:

My name is John Smith and I am 25 years old.

String interpolation can be used to display any valid TypeScript expression, including concatenation of two or more strings or accessing properties of an object:

<h4>Welcome to {{'Angular ' + version}}!</h4>
<h4>Your profile picture is {{user.profile.pictureUrl}}.</h4>

The first string interpolation will display the text "Welcome to Angular X.X.X!" where X.X.X is the version of Angular used in the application. The second string interpolation will display the URL of the profile picture of the user.

String interpolation is a simple and powerful feature in Angular 8 that makes it easy to display values from TypeScript code in the component's template.

Reasons Why Angular 8 Components are Essential

Angular 8 components help to organize and structure web applications into modular and reusable parts. The following are the reasons why Angular 8 components are crucial:

  • Modularity: Angular 8 components allow you to create independent and reusable modules that can be integrated into other parts of the application, making it easier to maintain and scale the app.
  • Reusability: Angular 8 components can be reused in many different parts of your application, which reduces the amount of code you need to write, and thereby saving you time and effort.
  • Maintainability: With Angular 8 components, it is easier to maintain your code because each component has its own code, styles, and templates, making it easier to fix bugs or make updates.
  • Testability: Components in Angular 8 can be tested in isolation, which makes it easier to troubleshoot and debug issues in your application, ensuring it is of high quality.

Understanding NgModules in Angular 8

In Angular 8, NgModule is a decorator function that is used to define the metadata for an Angular module. A module is a logical collection of components, directives, pipes, services, and other modules, which can then be used to organize an application into functional blocks.

NgModules allow developers to organize an application into functional modules with well-defined boundaries and clear dependencies. This makes it easier to manage and maintain large, complex applications, as well as enabling code reusability.

NgModules specify which components, directives, pipes and services are available to other components, as well as defining how they are imported and exported from the module. They also control which dependencies are included in the module, and can be used to provide configuration options and initialization code.

Overall, understanding NgModules is essential for building scalable and maintainable applications with Angular.

Explanation of Event Binding with an Example

Event binding refers to the process of attaching a function or handler to an event that triggers when a certain action occurs, such as clicking a button, hovering over an element, or submitting a form.

For instance, consider the following HTML code:

<button id="myBtn">Click me!</button>

To bind an event to this button and take some action when it's clicked, you can use JavaScript code as follows:

const button = document.getElementById('myBtn');
button.addEventListener('click', function() {
  console.log('Button clicked!');

In the above example: - We first select the button element using its ID "myBtn" - We then use the `addEventListener()` method to attach an event listener to the button. - The `click` event is passed as the first argument to `addEventListener()`, indicating that the event we want to handle is a click. - Finally, we pass a function as the second argument to `addEventListener()`. This function will be called whenever the button is clicked.

The function in this example logs a message to the console when the button is clicked, but you can perform any action you want inside this function.

This is just one example of how event binding can be used to add interactivity to a web page and respond to user actions.

Why Applications Compiled with AOT Launch Faster?

Applications that are compiled with AOT (Ahead of Time Compilation) generally launch faster due to the fact that all of the necessary code and dependencies are pre-compiled into machine code during the build process. This means that when the application is launched, the code is already in a format that can be executed by the machine, eliminating the need for further compilation at runtime. As a result, the application can start up more quickly and with less overhead compared to Just-In-Time (JIT) compiled applications that require compilation during runtime.

// Sample code of AOT-compiled application
int main() {
  // pre-compiled code here
  return 0;

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