JavaScript Interview Questions

Level up your JavaScript skills for your next frontend interview! This guide covers essential theory and practical coding questions to ace that interview. We'll explore JavaScript's quirks and intricacies, preparing you for those tough interview challenges.

We've categorized the questions into two key areas:

Theoretical Foundations: This section tests your understanding of core JavaScript concepts. Expect questions on fundamental topics like the event loop, inheritance, prototypes, and more. Think of it as a deep dive into JavaScript's philosophical underpinnings.

Practical Coding Challenges: Here's where you'll put your coding skills to the test. Prepare to build features, solve coding puzzles, and wrestle with asynchronous operations using promises and async/await. We'll even dissect a real-world interview example to give you a taste of what to expect.

Let's dive in! This comprehensive guide focuses on must-know JavaScript interview topics.

Core JavaScript Concepts:

1. JavaScript Data Types: List and explain the various data types in JavaScript.

2. Hoisting Explained: Detail how hoisting works in JavaScript, including the differences between arrow functions and regular functions. (Note: Normal functions are fully hoisted; arrow functions are not.)

3. var, let, and const: Explain the differences between these three keywords in terms of scope and reassignment.

4. Pass-by-Value vs. Pass-by-Reference: Clarify the distinction between pass-by-value and pass-by-reference in JavaScript, and how it relates to primitive and non-primitive data types. (Hint: Primitives are pass-by-value; objects are pass-by-reference.)

5. Deep Copy vs. Shallow Copy: Describe the difference between creating a deep copy and a shallow copy of an object.

6. Immediately Invoked Function Expressions (IIFEs): Explain the purpose and syntax of IIFEs (Self-Invoking Functions). Example:

<code class="language-javascript">(function () {
    console.log("I am a self-invoking function!");
})();</code>

7. JavaScript Strict Mode: Describe the benefits and implications of using strict mode in JavaScript.

8. Higher-Order Functions: Explain what higher-order functions are and provide examples.

9. The this Keyword: Explain the behavior of the this keyword in different JavaScript contexts.

10. call(), apply(), and bind(): Explain the functionality and usage of these three methods.

11. Currying in JavaScript: Define and illustrate currying in JavaScript.

12. Lexical Scoping: Explain lexical scoping (static scoping) in JavaScript.

13. Closures: Explain the concept of closures in JavaScript.

14. Object Prototypes: Describe the role and purpose of object prototypes.

15. Prototypal Inheritance: Explain prototypal inheritance in JavaScript.

16. Callbacks: Define and give examples of callbacks in JavaScript.

17. Callback Hell: Explain what callback hell is and how to avoid it.

18. Rest Parameter vs. Spread Operator: Explain the differences between the rest parameter (...) and the spread operator (...).

19. Promises: Describe the purpose and usage of Promises in JavaScript.

20. Generator Functions: Explain what generator functions are and how they work.

21. Temporal Dead Zone (TDZ): Explain the Temporal Dead Zone in JavaScript.

22. async and await: Explain the use of async and await for asynchronous operations.

23. reduce() Function: Explain the functionality and usage of the reduce() array method.

24. Implicit Coercion: Explain implicit type coercion in JavaScript and its potential pitfalls.

25. First-Class Citizens: Explain what it means for functions to be "first-class citizens" in JavaScript.

26. Scope of this inside an Object: Describe the behavior of this within an object and nested functions.

27. The new Keyword: Explain the significance of the new keyword when creating objects.

28. Memoization: Explain the concept of memoization and how it can improve performance.

29. Map, WeakMap, and WeakSet: Describe the differences and use cases for these data structures.

30. Event Propagation: Explain event propagation (capturing and bubbling) in JavaScript.

31. Event Delegation: Explain event delegation in JavaScript.

32. Event Loop: Describe the JavaScript event loop mechanism.

33. Control Flow: Explain different control flow structures in JavaScript (if/else, switch, loops).

34. SSR vs. CSR: Compare and contrast Server-Side Rendering (SSR) and Client-Side Rendering (CSR).

35. Declarative vs. Imperative Programming: Explain the difference between declarative and imperative programming styles.

36. Debouncing and Throttling: Explain the techniques of debouncing and throttling and their applications.

Coding Challenges:

1. String Reversal: Write a JavaScript function to reverse a string.

2. Debouncing Function: Implement a debounce function.

3. Throttling Function: Implement a throttle function.

4. Sorting Objects: Write a function to sort an array of objects based on a specified key.

5. Constructor Function: Create a constructor function for a simple object (e.g., a Person object).

6. Polyfills for map, reduce, and filter: Create polyfills for the map, reduce, and filter array methods.

7. Asynchronous Execution with setTimeout: Write three functions using setTimeout with different delays, and then execute them sequentially.

8. Simple Callback Function: Demonstrate the use of a callback function.

9. Curried multiply Function: Create a curried multiply function that works as shown below:

<code class="language-javascript">(function () {
    console.log("I am a self-invoking function!");
})();</code>

10. Memoization Implementation: Implement a memoization function for a simple operation (e.g., addition).

This expanded guide provides a more comprehensive and detailed preparation for your JavaScript interview. Remember to practice coding these examples and thoroughly understand the theoretical concepts. Good luck!

For even more practice, check out this helpful GitHub repository: https://www.php.cn/link/cdad431591373e47eba5ab6c984c2b55

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