JavaScript Advanced Functions - Practice Questions 2026

Detailed Feedback Loops: Every single question is accompanied by an exhaustive explanation, ensuring you learn from every mistake.

Industry Standards: The questions are modeled after real-world technical interviews at top-tier tech companies.

Core Concepts: This section dives into the mechanics of Scope and Hoisting. You will be tested on how JavaScript handles variable accessibility and function availability during the creation phase.

Intermediate Concepts: Here, we explore Closures and Higher-Order Functions. You will learn to identify how functions retain access to their lexical environment even after the outer function has closed.

Advanced Concepts: This level covers complex topics like Currying, Function Composition, Recursion, and the explicit binding of "this" using Call, Apply, and Bind.

Real-world Scenarios: You will encounter questions based on common development tasks, such as debouncing, throttling, and managing asynchronous function flows.

Mixed Revision / Final Test: A comprehensive evaluation that pulls questions from every category to simulate a high-stakes certification or interview environment.

OPTION 2: 1

OPTION 3: 2

OPTION 4: undefined

OPTION 5: ReferenceError

CORRECT ANSWER: OPTION 3

CORRECT ANSWER EXPLANATION: This is a classic example of a Closure. When outer() is called, it returns the inner function. The variable count is preserved in the inner function's lexical environment. The first call instance() increments count to 1. The second call, which is inside the console. log(), increments it to 2 and returns that value.

WRONG ANSWERS EXPLANATION:

OPTION 2: Incorrect because this would be the result of the first call only.

OPTION 4: Incorrect because the function explicitly returns the variable count.

OPTION 5: Incorrect because count is properly defined within the scope of the outer function.

OPTION 2: Function. prototype. apply()

OPTION 3: Function. prototype. call()

OPTION 4: Function. prototype. map()

OPTION 5: Function. prototype. slice()

CORRECT ANSWER: OPTION 2

CORRECT ANSWER EXPLANATION: The apply() method calls a function with a given this value, and arguments provided as an array (or an array-like object). This allows the elements of the array to be treated as individual arguments to the function.

WRONG ANSWERS EXPLANATION:

OPTION 3: call() accepts an argument list, not an array. To use an array with call(), you would need to use the spread operator.

OPTION 4: map() is an Array prototype method used for learn ai for enterprise transformation a roadmap for leaders, not for changing function execution context.

OPTION 5: slice() is used to extract a portion of an array and has no relation to function invocation.

This is a huge original question bank.

You get support from instructors if you have questions.

Each question has a detailed explanation.

Mobile-compatible with the Udemy app.

30-days money-back guarantee if you're not satisfied.