Master Your JavaScript Skills with This Quick Functions and Closures Quiz!

Test your JavaScript knowledge with this quick quiz! Covers function declarations vs function expressions, arrow functions, closures, scope, higher-order functions, and output-based questions.

Question 1.

What is the output of this code?

function sayHi() { console.log(name); var name = "John"; } sayHi();

A.
John
B.
undefined
C.
ReferenceError
D.
null

Question 2.

Which of the following is a correct syntax for an arrow function?

A.
const sum = (a, b) => { return a + b; }
B.
const sum = (a, b) { return a + b; }
C.
const sum => (a, b) => return a + b;
D.
const sum = a, b => a + b;

Question 3.

What is the output of this closure example?

function outer() { let count = 0; return function inner() { count++; console.log(count); }; } const counter = outer(); counter(); counter();

A.
1 and 2
B.
0 and 0
C.
undefined
D.
1 and 1

Question 4.

What is an IIFE in JavaScript?

A.
A function with no parameters
B.
A function that is hoisted
C.
A function that calls itself automatically
D.
A function with this context

Question 5.

What will be logged in the console?

const greet = (function(name) { return `Hello, ${name}`; })("Alice"); console.log(greet);

A.
Hello, Alice
B.
undefined
C.
Hello,
D.
ReferenceError

Question 6.

What will console.log(sum); output?

var sum = function(a, b) { return a + b; }; console.log(sum(2, 3));

A.
undefined
B.
TypeError
C.
ReferenceError
D.
5

Question 7.

What will happen here?

const arrowFunc = () => { console.log(this); }; arrowFunc();

A.
undefined
B.
window or global object
C.
null
D.
Error

Question 8.

What is the output?

function example() { var a = 10; function inner() { console.log(a); } a = 20; return inner; } const result = example(); result();

A.
undefined
B.
10
C.
20
D.
Error

Question 9.

Which higher-order function is used to transform each element of an array?

A.
forEach()
B.
filter()
C.
reduce()
D.
map()

Question 10.

What is the result of this code?

const arr = [1, 2, 3, 4]; const result = arr.filter(num => num % 2 === 0).map(num => num * 2); console.log(result);

A.
[2, 4, 6, 8]
B.
[4, 8]
C.
[2, 4]
D.
[8, 4]