Top 10 Angular Interview Questions — Plus Answers

8 minutes

One of the best ways to prepare for a technical interview is to practice answering the questions you think you’ll be asked during your interview. You can do this on your own or ask a friend to do a mock interview with you so you can practice answering questions out loud in front of someone. If you’re able to spend a few hours doing this, it’s less likely that you’ll be caught off guard by challenging questions. This also helps build your confidence going into a potentially high-stakes interview.

If you’re interested in a career that involves building dynamic websites, proficiency in Angular, the open-source framework created and maintained by Google, is a sought-after technical skill. When you’re interviewing for roles like Full-Stack Engineer and Front-End Engineer, it’s likely that you’ll be asked a handful of Angular-specific questions. If you’re looking for commonly asked Angular interview questions to practice, here are 10 popular ones to help you land your next role.

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1. How does an Angular application work?

Angular applications work by storing all of the configurations of the app in a single file named angular.json. When building the app, this file tells the builder the entry point of the application. This creates a browser environment for the application to run and then calls a function to bootstrap the application. The application being bootstrapped is declared within a specific module in the file, which holds declarations of all of the components for the application.

Each component is declared with a Selector, a Template or TemplateURL, and a StylesURL. These provide information on how to access the component, the HTML of the component, and any style sheets specific to that component.

Finally, Angular calls the index.html file, which calls the root component (defined in the app.component.ts, inside the <app-root> tags), and in this way, the file serves all of the necessary data to the webpage to run the application.

2. Why was Angular introduced?

Before Angular was introduced as a client-side framework, developers generally used VanillaJS and jQuery when developing dynamic websites. But issues started to come up as websites became more complicated in both features and functionality. The code became harder to maintain and there was no provision of data handling facilities across the views by jQuery.

Angular was created to solve these pain points by dividing code into smaller portions of information (known as Components). Angular is a client-side framework, letting users develop advanced web applications (like SPAs) much faster than using VanillaJS.

3. What are some of the advantages of Angular over other frameworks?

Because ease of use is at the core of its design, Angular has a number of advantages over other frameworks. Many built-in features are provided straight “out of the box” (without needing to look for them separately), such as routing, state management, rxjs library, and HTTP services.

Angular uses HTML to render the UI of an application, which is easier to use than JavaScript. Additionally, Angular has excellent community support. Google has also announced long-term support for Angular, showing their commitment to using this framework and their intent to further scale up the ecosystem.

4. What are the differences between AngularJS and Angular?

For this question, answering with a brief high-level overview can help show your ability to speak on a complex topic succinctly. Your answer could discuss how AngularJS (Angular JavaScript) and Angular use different command and operating languages. AngularJS uses the JavaScript language and MVC (Model-View-Controller) design model, while Angular uses the TypeScript language with components and directives.

But the interviewer will likely expect you to go deeper into the differences. You can mention key differences in the architecture, language, structure, expression syntax, and ability to support mobile devices. For mobile support, Angular is supported by all popular mobile browsers, while AngularJS is not.

If you want to talk about the language differences, you can mention how AngularJS uses a dynamically typed language, while Angular uses a statically typed language that generally performs better for developing larger applications. For expression syntax, AngularJS requires developers to remember the precise ng-directive for binding any event or property. Angular uses much simpler attributes for property binding and event binding, making it far easier on the developer.

For differences in the architecture, Angular uses Components instead of Controllers, which act as directives, and AngularJS uses a MVC architecture with a:

  • Model for business logic
  • Controller for processing information
  • and View for showing the information that’s in the Model.

For structure differences, the bigger the application, the more complicated and time-consuming maintaining code is in AngularJS. And by comparison, maintaining code for large applications in Angular is far easier thanks to its structure.

5. What is AOT compilation in Angular?

AOT (Ahead-of-Time) compilation refers to the application compiling during the build time, as opposed to JIT (Just-in-Time) compilation in which the application compiles inside the browser during runtime.

Angular applications need to use AOT compilation because they include components and templates that, by default, a browser isn’t able to understand. AOT compilation allows the Angular application to compile before running inside the browser. This means that the Angular compiler will take in the JS code, compile it, and then produce JS code.

This action allows for extremely fast rendering, as the browser can load and render the executable code immediately because the application is already compiled. It also cuts down on AJAX requests for source files, because the compiler sends HTML and CSS files with the application.

Because the AOT compiler adds HTML and templates into the JS files before the application runs inside the browser, it leaves no extra HTML files to be read. This improves security for the application as a whole.

6. Explain the ways to achieve data binding in Angular

Data binding is used to connect application data with the DOM (Data Object Model). There are four main forms of data binding in Angular:

  1. Event binding. This enables the application to respond to user input in the target environment.
  2. Property binding. This enables the interpolation of values computed from application data into the HTML.
  3. Two-way binding. This uses the ngModel directive to automatically reflect application state changes to the view and vice versa.
  4. String interpolation binding. This uses template expressions to display component data. It’s also known as “mustache syntax” because the template expressions are enclosed in curly braces, {{ }}.

7. What are decorators and annotations? What is the difference between them?

In Angular, decorators refer to the design patterns that separate decoration or modification of a class without altering the source code. A decorator adds metadata to a class, object, or method. An annotation is a hard-coded feature that reflects the metadata library. When set on the class, it creates an annotation array that is stored in that class within an attribute called “annotations” and passes the metadata into the constructor. Decorators are predefined, while annotations are not.

8. What are expressions in Angular, and how are they different from JavaScript expressions?

Angular expressions bind application data to HTML. When the expression is resolved, it returns the result to where the expression is written. Angular expressions let the user write JavaScript in HTML.

While Angular expressions and JavaScript expressions are both written within braces, there are some key differences between them. Angular expressions are evaluated against the locally scoped object, rather than the global window object. When using an Angular expression, you won’t be able to access a property outside of its local scope.

Angular expressions can accommodate null and undefined values, unlike JavaScript expressions. Finally, Angular expressions leverage pipes to format data before it’s displayed, rather than using any loops, conditionals, or exceptions.

9. What are the lifecycle hooks of Angular?

When a component is created, it cycles through its own life cycle of phases. Lifecycle hooks in Angular are used to check where a component is in its life cycle and to trigger changes at a specific phase Specific lifecycle hooks include:

  • ngOnChanges( ): Called when input properties of the component are changed.
  • ngOnInit( ): Called after the ngOnChanges hook, to initialize the component and set the input properties.
  • ngDoCheck( ): Called to detect and act on changes.
  • ngAfterContentInit( ): Called after the first ngDoCheck hook, to respond after the content is projected inside the component.
  • ngAfterContentChecked( ): Called after ngAfterContentInit (and every subsequent ngDoCheck) to respond after the projected content is checked.
  • ngAfterViewInit( ): Called after a component’s view, or after initializing a child component’s view.
  • ngAfterViewChecked( ): Called after ngAfterViewInit, to respond when the component’s view or child component’s view is checked.
  • ngOnDestroy( ): Called immediately before destroying the component, to clean up the code and detach the event handlers.

10. What are directives in Angular?

Directives in Angular are classes that can be imported into components. These are often used when multiple components in an application need to have similar functionality. Rather than adding the same functionality to every component manually, the developer can create one directive with the functionality and import it to all of the relevant components. Every directive has its own behavior and is declared using the @Directive decorator. Three types of directives used in Angular include component directives, structural directives, and attribute directives.

More interview prep and resources

Need a refresher on any of the Angular concepts we covered here? If so, check out our Learn AngularJS course where you’ll apply your HTML and JavaScript skills and learn how to build single-page web applications. This course also covers the Model-View-Controller (MVC) programming pattern. 

If you’re looking for more support and resources for your interviews, our complete guide to the technical interview is full of tips and advice that make it easier to knock your interviews out of the park. Our advice on answering behavioral interview questions is another good article to review. And our Career Center offers even more job-hunting resources, from resume writing to networking to building a great portfolio. And if you’re looking to learn a new skill or take one of your existing skills to the next level, check out our full catalog for courses on web development, math, data science, programming languages, and more.

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