AngularJS 1 Interview Questions with Expert Answers

Despite newer Angular versions taking center stage, AngularJS (version 1.x) remains relevant in many enterprise applications. Developers interviewing for front-end positions often encounter AngularJS questions, especially when companies maintain legacy systems. Being prepared with expert answers to common AngularJS interview questions can significantly boost your chances of success.

Top AngularJS 1 interview questions and expert answers

1. What are scopes and how do they work in AngularJS 1?

In AngularJS, scopes are JavaScript objects that reference the application model. They serve as the glue between controllers and views, creating a connection that enables data manipulation. Scopes are arranged in a hierarchical structure mirroring the DOM structure of your application, allowing for inheritance of properties from parent to child scopes.

2. Explain the difference between $watch, $digest, and $apply

$watch: Observes changes to expressions, taking a watchExpression and a listener function that executes when changes occur.

$digest: AngularJS’s internal cycle that checks for changes in watched expressions within the current scope and its children.

$apply: Explicitly starts the $digest cycle from the root scope, ensuring the entire application updates when changes occur outside AngularJS’s context.

3. How do directives work and when to create a custom one?

Directives extend HTML with new attributes and elements, enabling dynamic UI components. Create custom directives when you need direct DOM manipulation, want reusable components, or need to integrate third-party libraries.

More than 6,700 companies, including Google and Amazon, use AngularJS in their tech stacks [Educative].

4. What is two-way data binding in AngularJS 1 and how does it work?

Two-way data binding creates automatic synchronization between the model and view. When model data changes, the view updates instantly, and when users modify the view, the model updates automatically. This happens through a compiler that processes directives and the digest cycle that tracks changes.

AngularJS developers can earn between $90,000 to $120,000 in the U.S. [CRS Info Solutions].

5. How does dependency injection work in AngularJS 1?

Dependency Injection in AngularJS allows components to receive dependencies instead of creating them. The injector subsystem creates dependencies, while services act as singletons. AngularJS supports multiple annotation methods (inline, $inject property, array notation) to specify dependencies.

6. What are some key differences between AngularJS 1 and Angular 2+?

• Language: JavaScript vs. TypeScript
• Architecture: MVC pattern vs. component-based
• Performance: Angular 2+ is 5 times faster
• Binding: Different syntax for property and event binding
• Structure: Controllers/scopes vs. components/services
• Mobile Support: Angular 2+ has better mobile optimization

7. How would you handle performance issues in large AngularJS apps?

• Use one-time binding (::) to reduce watchers
• Limit watchers per page (keep under 2,000)
• Implement debouncing for frequent events
• Use track by with ng-repeat for optimized list rendering
• Leverage controller lifecycle hooks ($onInit, $onDestroy)
• Consider lazy loading for non-essential modules

8. What are services, factories, and providers in AngularJS 1?

Services: Singleton objects created with the ‘new’ operator that return instantiated objects.

Factories: Functions that create and return objects or functions.

Providers: The most configurable service type, the only one available in the app.config phase.

The latest stable AngularJS version is v1.8.2 (October 2020) [InterviewBit].

9. How do you test AngularJS 1 controllers and services?

Testing typically involves Jasmine or Mocha for unit tests, Karma as the test runner, and angular-mocks to inject dependencies. The $controller service instantiates controllers for testing, while mock services replace real dependencies to isolate components.

10. Explain how routing works in AngularJS 1 using ngRoute or ui-router

ngRoute: The official routing module supporting basic routing with templates and controllers, configured via $routeProvider.

ui-router: A more powerful third-party solution supporting nested views and states instead of routes, ideal for complex applications with multiple views.

Both map URLs to controllers and templates, enabling single-page application navigation without page reloads.

Conclusion

Mastering these AngularJS interview questions demonstrates your understanding of this important framework. While newer versions continue to evolve, many companies still maintain AngularJS applications, making these skills valuable. Remember that real-world experience and understanding the “why” behind each feature are just as important as memorizing answers.

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