Whether you’re a fresh graduate or an experienced developer, these are some of the most important JavaScript interview questions that often come up. This guide gives you clear and concise answers to each.
JavaScript continues to be one of the most essential and in-demand programming languages for modern web development. Whether you’re preparing for a frontend, backend, or full-stack developer role, a solid understanding of JavaScript concepts is crucial. In this post, we’ve compiled a list of the most commonly asked JavaScript interview questions — along with concise and clear answers — to help you crack your next interview with confidence.
1.Can you name two programming paradigms important for JavaScript app developers?
Answer:
The two major paradigms are:
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Object-Oriented Programming (OOP): Uses objects and classes to model real-world entities.
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Functional Programming (FP): Emphasizes immutability, pure functions, and avoiding side effects.
2.What is functional programming?
Answer:
Functional programming is a paradigm where computation is treated as the evaluation of mathematical functions. It avoids shared state, mutable data, and side effects. Key features include:
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Pure functions
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Higher-order functions
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First-class functions
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Immutability
3.What is the difference between classical inheritance and prototypal inheritance?
Answer:
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Classical Inheritance: Based on classes. Objects are instances of classes. Common in languages like Java and C++.
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Prototypal Inheritance: Used in JavaScript. Objects inherit directly from other objects via a prototype chain.
4.What are the pros and cons of functional programming vs. object-oriented programming?
Answer:
| Feature | Functional Programming | Object-Oriented Programming |
|---|---|---|
| Pros | More predictable, easier testing, avoids side effects | Better code reuse, models real-world objects |
| Cons | Can be harder to understand at first | Can lead to complex hierarchies and tight coupling |
5.When is classical inheritance an appropriate choice?
Answer:
When your application has a well-defined and stable hierarchy (e.g., GUI frameworks), and you benefit from sharing methods via a class structure.
6.When is prototypal inheritance an appropriate choice?
Answer:
When you need flexibility and dynamic extension of objects. It’s ideal for situations where class-based structures are too rigid or unnecessary.
7.What does “favor object composition over class inheritance” mean?
Answer:
This means instead of building deep inheritance trees, you should build small, reusable objects and combine them to create complex behaviors. Composition promotes more flexible and maintainable code.
8.What are two-way data binding and one-way data flow, and how are they different?
Answer:
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Two-way data binding: Changes in the UI update the model, and changes in the model update the UI automatically (e.g., AngularJS).
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One-way data flow: Data flows in one direction — from model to view. UI changes require explicit handling (e.g., React).
Difference: One-way is more predictable and easier to debug. Two-way can be simpler to implement in small apps but harder to maintain at scale.
9.What are the pros and cons of monolithic vs. microservice architectures?
Answer:
| Architecture | Pros | Cons |
|---|---|---|
| Monolithic | Easier to develop/test initially, less operational overhead | Hard to scale, difficult to maintain as app grows |
| Microservices | Scalable, independent deployment, better fault isolation | Complex deployment, inter-service communication overhead |
10.What is asynchronous programming, and why is it important in JavaScript?
Answer:
Asynchronous programming allows JavaScript to perform long network or I/O tasks (like fetching data) without blocking the main thread. It uses callbacks, promises, or async/await to handle operations efficiently, improving performance and responsiveness in web apps.
Conclusion:
JavaScript interviews often test not just your coding skills, but your understanding of concepts and how you apply them in real-world applications. Reviewing these questions will not only prepare you for interviews but also strengthen your development skills overall. Keep practicing, stay curious, and never stop learning — because that’s what makes a great developer
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