JavaScript Functional Programming - Practice Questions 2026 - Free Online Course

Master the art of clean, predictable, and maintainable code with our comprehensive JavaScript Functional Programming Practice Exams. This course is specifically designed for developers who want to move beyond imperative programming and embrace the power of pure functions, immutability, and declarative logic.

Why Serious Learners Choose These Practice Exams

Serious learners understand that watching tutorials is only half the battle. To truly master functional programming (FP), you must test your ability to read, debug, and write FP-style code under pressure. Our question bank is meticulously crafted to simulate real-world coding challenges and technical interview scenarios. We focus on shifting your mindset from "how to do it" to "what to solve," ensuring you understand the underlying mathematical principles that make JavaScript FP so robust.

Course Structure

Our practice exams are divided into logical tiers to ensure a smooth learning curve:

Basics / Foundations: This section focuses on the essential building blocks. You will be tested on the definition of pure functions, the importance of side-effect-free code, and the fundamental differences between imperative and declarative styles.
Core Concepts: Here, we dive into the "Big Three" of functional JavaScript: Map, Filter, and Reduce. You will practice transforming data structures without mutating the original source, ensuring you understand the concept of immutability.
Intermediate Concepts: This module covers Currying, Partial Application, and High-Order Functions. You will learn how to create specialized functions from generic ones and how to pass functions as arguments to build modular logic.
Advanced Concepts: Challenge yourself with Function Composition, Monads, and Recursion. This section tests your ability to chain multiple functions together to create complex data pipelines while maintaining code readability.
Real-world Scenarios: Apply your knowledge to practical situations. These questions involve refactoring messy "spaghetti code" into clean functional components, handling API responses, and managing state in a functional manner.
Mixed Revision / Final Test: A comprehensive, timed exam that pulls from all previous sections. This is designed to verify your readiness for professional projects or high-level technical interviews.

Sample Practice Questions

Question 1

What will be the output of the following code snippet?

const numbers = [1, 2, 3];

const result = numbers. map(x => x * 2).filter(x => x > 2);

console.log(numbers);

Option 1: [2, 4, 6]
Option 2: [4, 6]
Option 3: [1, 2, 3]
Option 4: [2, 3]
Option 5: Undefined

Correct Answer: Option 3

Correct Answer Explanation: Functional programming emphasizes immutability. The .map() and .filter() methods do not change the original array; they return new arrays. Since the console.log is targeting the original numbers variable, it remains [1, 2, 3].

Wrong Answers Explanation:

Option 1: This is the result after the map operation, but it is a new array, not the original.
Option 2: This is the final value of the result variable, not the numbers variable.
Option 4: This represents a misunderstanding of how the filter logic and mapping logic interact.
Option 5: The variable numbers is clearly defined and remains in scope, so it cannot be undefined.

Question 2

Which of the following best describes a "Pure Function"?

Option 1: A function that uses a global variable to calculate its result.
Option 2: A function that always returns the same output for the same input and has no side effects.
Option 3: A function that modifies an object passed to it as a reference.
Option 4: A function that performs an asynchronous API call before returning a value.
Option 5: A function that must contain a console.log to be valid.

Correct Answer: Option 2

Correct Answer Explanation: A Pure Function is the cornerstone of FP. It is deterministic (same input = same output) and does not interact with or modify the outside world (no side effects).

Wrong Answers Explanation:

Option 1: Using global variables makes a function impure because the output can change if the global variable changes outside the function's control.
Option 2: Modifying an object by reference is a "side effect" (mutation), which violates the rules of pure functions.
Option 4: API calls are unpredictable and depend on network state, making the function impure.
Option 5: console. log is actually a side effect because it modifies the state of the console/terminal. While useful for debugging, it technically makes a function impure.

Welcome to the best practice exams to help you prepare for your JavaScript Functional Programming.