MCQs on Advanced Functions and Scope | JavaScript Intermediate

Dive deep into closures, lexical scope, higher-order functions, callbacks, and IIFE to enhance your JavaScript skills and write optimized, maintainable, and powerful code.

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Closures and Lexical Scope (8 MCQs)

1. What is a closure in JavaScript?
   • A) A function bundled with its lexical environment
   • B) A method to close an open file
   • C) A block of code executed immediately
   • D) A syntax for declaring variables
2. Which of the following is a key feature of closures?
   • A) They can modify variables declared in their outer scope
   • B) They do not allow variable sharing
   • C) They execute outside their lexical environment
   • D) They can only be called once
3. What determines the lexical scope of a function in JavaScript?
   • A) The function’s arguments
   • B) Where the function is defined in the code
   • C) The function’s name
   • D) The browser’s JavaScript engine
4. How can closures be used in JavaScript?
   • A) To prevent memory leaks
   • B) To create private variables
   • C) To execute code asynchronously
   • D) To modify the global object
5. Which of the following scenarios demonstrates a closure?
   • A) A function that calls another function inside its body
   • B) A function that returns another function and uses variables from the outer scope
   • C) A function that has no parameters
   • D) A function that calls itself recursively
6. What happens to the variables used in a closure after the outer function has executed?
   • A) They are deleted immediately
   • B) They remain accessible through the closure
   • C) They are moved to the global scope
   • D) They are inaccessible
7. Which of the following best describes lexical scope?
   • A) Scope determined at runtime based on the call stack
   • B) Scope determined during the declaration phase
   • C) Scope that can be modified dynamically
   • D) Scope limited to local variables only
8. What is the output of this code?javascriptCopy codefunction outer() { let count = 0; return function inner() { count++; return count; }; } const counter = outer(); console.log(counter()); // ? console.log(counter()); // ?
   • A) 1, 2
   • B) 0, 1
   • C) 2, 2
   • D) Error

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Higher-Order Functions (8 MCQs)

9. What is a higher-order function in JavaScript?
   • A) A function that returns an object
   • B) A function that accepts or returns another function
   • C) A function with nested loops
   • D) A function declared with the async keyword
10. Which of the following is an example of a higher-order function?

• A) A function that calculates the square root
• B) Array.map()
• C) Math.pow()
• D) A function that declares a variable

11. Why are higher-order functions important in JavaScript?

• A) They enhance performance
• B) They reduce code redundancy
• C) They enable functional programming techniques
• D) All of the above

12. Which of the following functions is not considered a higher-order function?

• A) Array.forEach()
• B) Array.reduce()
• C) console.log()
• D) Array.filter()

13. How do higher-order functions achieve reusability?

• A) By creating multiple objects
• B) By abstracting common logic into reusable components
• C) By avoiding recursion
• D) By using var instead of let

14. What does the following code return?

javascriptCopy codeconst multiply = (a) => (b) => a * b;
const double = multiply(2);
console.log(double(5));

• A) 7
• B) 10
• C) 25
• D) 2

15. How does Array.reduce() work as a higher-order function?

• A) It combines all elements into a single value based on a callback function
• B) It filters elements from an array
• C) It modifies each element in place
• D) It executes functions asynchronously

16. What is the benefit of using Array.map() in conjunction with arrow functions?

• A) It simplifies code readability
• B) It prevents runtime errors
• C) It reduces array length
• D) It automatically filters out duplicates

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Callback Functions (8 MCQs)

17. What is a callback function in JavaScript?

• A) A function that is executed immediately upon declaration
• B) A function passed as an argument to another function
• C) A function that runs in the global scope
• D) A function without a return value

18. Which of the following scenarios demonstrates the use of a callback function?

• A) Logging a message after data is fetched from an API
• B) Declaring a variable
• C) Using Math.random()
• D) Executing code inside a for loop

19. What does the following code demonstrate?

javascriptCopy codefunction greet(name, callback) {
    console.log(`Hello, ${name}`);
    callback();
}
greet("Alice", () => console.log("Welcome!"));

• A) Asynchronous programming
• B) Callback functions
• C) Higher-order functions
• D) Promises

20. How can callback functions lead to “callback hell”?

• A) By reducing code readability when nested deeply
• B) By using arrow functions incorrectly
• C) By causing infinite loops
• D) By breaking the call stack

21. Which method uses callback functions for asynchronous operations?

• A) fetch()
• B) setTimeout()
• C) Promise.then()
• D) All of the above

22. What is the output of the following code?

javascriptCopy codesetTimeout(() => console.log("First"), 0);
console.log("Second");

• A) First, Second
• B) Second, First
• C) First only
• D) Error

23. How can callback functions be avoided in modern JavaScript?

• A) By using IIFE
• B) By using Promises or async/await
• C) By using closures
• D) By using synchronous code only

24. What is the primary purpose of using a callback function?

• A) To make code run faster
• B) To handle asynchronous tasks
• C) To avoid recursion
• D) To modify global variables

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IIFE (Immediately Invoked Function Expression) (6 MCQs)

25. What is an IIFE in JavaScript?

• A) A function invoked as soon as it is defined
• B) A function that cannot be reused
• C) A type of closure
• D) A global function

26. What is the main benefit of using an IIFE?

• A) To define private variables
• B) To increase runtime performance
• C) To reduce memory usage
• D) To modify the global object

27. How is an IIFE written in JavaScript?

javascriptCopy code(function() {
    console.log("Hello!");
})();

• A) Correct syntax
• B) Incorrect syntax
• C) Asynchronous declaration
• D) Deprecated syntax

28. Why are IIFEs often used in JavaScript modules?

• A) To initialize code without polluting the global scope
• B) To avoid using closures
• C) To reduce callback hell
• D) To reuse global variables

29. Which of the following is a valid example of an IIFE?

• A) function() {}();
• B) (function() {})();
• C) function() {}()();
• D) (function() {});

30. What is the scope of variables defined inside an IIFE?

• A) Global scope
• B) Local to the IIFE
• C) Lexical scope of the parent function
• D) Shared across all IIFEs

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Answers

Qno	Answer
1	A) A function bundled with its lexical environment
2	A) They can modify variables declared in their outer scope
3	B) Where the function is defined in the code
4	B) To create private variables
5	B) A function that returns another function and uses variables from the outer scope
6	B) They remain accessible through the closure
7	B) Scope determined during the declaration phase
8	A) 1, 2
9	B) A function that accepts or returns another function
10	B) Array.map()
11	D) All of the above
12	C) console.log()
13	B) By abstracting common logic into reusable components
14	B) 10
15	A) It combines all elements into a single value based on a callback function
16	A) It simplifies code readability
17	B) A function passed as an argument to another function
18	A) Logging a message after data is fetched from an API
19	B) Callback functions
20	A) By reducing code readability when nested deeply
21	D) All of the above
22	B) Second, First
23	B) By using Promises or async/await
24	B) To handle asynchronous tasks
25	A) A function invoked as soon as it is defined
26	A) To define private variables
27	A) Correct syntax
28	A) To initialize code without polluting the global scope
29	B) (function() {})();
30	B) Local to the IIFE