JavaScript Internals & Advanced Concepts

Question 1

What is an execution context in JavaScript?

Answer 1

It’s an abstract concept describing the environment where code is evaluated and executed, including scope, variables, and the value of ‘this’.

Question 2

What is the call stack?

Answer 2

The call stack is a data structure that tracks function invocation, executing the most recent function call first (LIFO).

Question 3

What is a closure in JavaScript?

Answer 3

A closure is a function that retains access to its lexical scope even after the outer function has finished executing.

Question 4

What is memory management in JavaScript?

Answer 4

It involves allocating and releasing memory for variables, objects, and functions used in the program.

Question 5

What is garbage collection in JavaScript?

Answer 5

It is the process of automatically reclaiming memory occupied by objects no longer reachable in the code.

Question 6

What is the difference between deep and shallow copy?

Answer 6

A shallow copy copies only top-level properties, while a deep copy recursively copies all nested properties.

Question 7

What is currying in JavaScript?

Answer 7

Currying is the process of breaking a function with multiple arguments into a series of functions that each take one argument.

Question 8

What is debouncing in JavaScript?

Answer 8

Debouncing delays a function’s execution until a certain time has passed since the last call.

Question 9

What is throttling in JavaScript?

Answer 9

Throttling limits a function to execute at most once in a specified period.

Question 10

What is an advantage of the call stack model?

Answer 10

It simplifies function invocation tracking and local execution context.

Question 11

What is a disadvantage of the call stack model?

Answer 11

Too many recursive calls can lead to stack overflow errors.

Question 12

What is an advantage of closures?

Answer 12

They enable private variables and maintain state across function calls.

Question 13

What is a disadvantage of closures?

Answer 13

They can cause memory leaks if references to outer scopes are not properly cleaned up.

Question 14

What is an advantage of automatic garbage collection?

Answer 14

It simplifies memory management for developers.

Question 15

What is a disadvantage of automatic garbage collection?

Answer 15

It can lead to non-deterministic memory cleanup, causing performance hiccups.

Question 16

What is a best practice with closures?

Answer 16

Avoid overusing closures in long-lived contexts to prevent memory leaks.

Question 17

What is a best practice with memory management?

Answer 17

Avoid global variables and detach event listeners when no longer needed.

Question 18

What is a best practice with deep vs shallow copies?

Answer 18

Use deep copies when working with nested objects that need to be independently modified.

Question 19

What is a best practice with debouncing and throttling?

Answer 19

Use debouncing for user input, and throttling for scroll or resize events.

Question 20

What is a use case for execution context and call stack?

Answer 20

Debugging function call chains and understanding async stack traces.

Question 21

What is a use case for closures?

Answer 21

Implementing data encapsulation and factory functions.

Question 22

What is a use case for garbage collection?

Answer 22

Freeing memory in long-running servers or applications to maintain performance.

Question 23

What is a use case for deep copy?

Answer 23

Cloning application state in Redux or similar state management libraries.

Question 24

What is a use case for currying?

Answer 24

Creating reusable, configurable functions in functional programming.

Question 25

What is a use case for throttling?

Answer 25

Limiting the frequency of API calls or event listeners in real-time apps.

Question 26

How does the call stack affect system design?

Answer 26

Impacts recursion depth, error tracing, and async execution flow.

Question 27

How do closures affect system design?

Answer 27

They can support modular architecture but may complicate debugging and memory profiling.

Question 28

What are architectural implications of memory management?

Answer 28

Efficient memory use is critical in high-load or long-lived Node.js applications.

Question 29

What is the architectural impact of debounce/throttle?

Answer 29

They optimize frontend responsiveness and reduce server load.

Question 30

Give an example of a closure.

Answer 30

function outer() { let count = 0; return function() { count++; return count; }; }

Question 31

Give an example of a shallow vs deep copy.

Answer 31

Shallow: let b = {...a}; Deep: let b = JSON.parse(JSON.stringify(a));

Question 32

Give an example of currying.

Answer 32

const add = a => b => c => a + b + c; add(1)(2)(3);

Question 33

Give an example of debounce.

Answer 33

function debounce(fn, delay) { let timeout; return (...args) => { clearTimeout(timeout); timeout = setTimeout(() => fn(...args), delay); }; }

Question 34

Give an example of throttle.

Answer 34

function throttle(fn, limit) { let inThrottle; return (...args) => { if (!inThrottle) { fn(...args); inThrottle = true; setTimeout(() => inThrottle = false, limit); } }; }

Question 35

How does call stack depth impact performance?

Answer 35

Deep stacks increase memory usage and risk stack overflows.

Question 36

How do closures affect memory usage?

Answer 36

They hold references to outer variables, which can cause memory leaks if not handled carefully.

Question 37

How does garbage collection affect performance?

Answer 37

Pauses for GC cycles can cause slight performance dips during cleanup.

Question 38

How do you monitor call stack usage?

Answer 38

Use DevTools or Node.js inspector to analyze stack traces and memory snapshots.

Question 39

How to debug closure-related bugs?

Answer 39

Use named functions, avoid unnecessary outer references, and inspect scope chains in DevTools.

Question 40

How to monitor memory usage in Node.js?

Answer 40

Use process.memoryUsage(), Chrome DevTools, or heap profiling tools.

Question 41

What is a real-world tradeoff with closures?

Answer 41

State persistence vs. potential for retained memory and leaks.

Question 42

What is a real-world tradeoff with garbage collection?

Answer 42

Ease of development vs. lack of precise control over memory cleanup.

Question 43

What is a real-world tradeoff with debounce/throttle?

Answer 43

Better performance vs. delayed or skipped execution events.

Question 44

Interview Question: What is the difference between stack and heap memory?

Answer 44

Stack memory stores primitives and call contexts, while heap stores objects and dynamic data.

Question 45

Interview Question: What are closures and how are they used?

Answer 45

Closures are inner functions that access outer function variables even after the outer function exits. Used in encapsulation, callbacks, and async handlers.

Question 46

Interview Question: What tools are used to analyze memory leaks in Node.js?

Answer 46

Chrome DevTools, Node.js built-in profiler, `heapdump`, and `memwatch-next`.

Question 47

Interview Question: When should you use deep copy instead of shallow copy?

Answer 47

When modifying nested structures that should not affect the original object.

Question 48

Interview Question: What is currying and why is it useful?

Answer 48

Currying transforms a function so it can be partially applied; useful for function reuse and composition.

Question 49

What is a gotcha with the call stack?

Answer 49

Infinite recursion or long sync loops can cause stack overflow errors.

Question 50

What is a gotcha with closures?

Answer 50

Retaining unintended variables in memory if closures are misused or not released.

Question 51

What is a gotcha with deep copy?

Answer 51

Using JSON.parse/stringify fails with functions, dates, or circular references.

Question 52

What is a gotcha with debounce/throttle?

Answer 52

Incorrect delay settings can make UI feel laggy or unresponsive.