Top JavaScript Interview Quiz: Key Concepts & Output-Based Questions

Test your JavaScript knowledge with this quick quiz! Covers essential concepts like array methods (map, filter, reduce), object destructuring, arrow functions and this, and error handling using try-catch. Perfect for developers preparing for JavaScript interviews or improving core programming skills!

Question 1.

What will the following code output?

const numbers = [1, 2, 3, 4]; const result = numbers.map(num => num * 2).filter(num => num > 5); console.log(result);

A.
[2, 4, 6, 8]
B.
[6, 8]
C.
[4, 6, 8]
D.
[12]

Question 2.

How do you access name from this object?

const person = { name: "John", age: 30 };

A.
person["name"]
B.
person.name
C.
Both A and B
D.
person[name]

Question 3.

What will this arrow function return?

const add = (a, b = 5) => a + b; console.log(add(10));

A.
10
B.
15
C.
NaN
D.
undefined

Question 4.

What is the value of this in the following code?

const obj = { method: () => console.log(this) }; obj.method();

A.
obj
B.
undefined
C.
Global object (window in browsers)
D.
null

Question 5.

Identify the error in this code:

try { console.log(x); } catch (error) { console.log("Error caught"); }

A.
x is not defined.
B.
The code will throw an uncaught error.
C.
Syntax error.
D.
No error; it will log "Error caught".

Question 6.

What will this code log?

const arr = [1, 2, 3]; const sum = arr.reduce((acc, curr) => acc + curr, 0); console.log(sum);

A.
6
B.
0
C.
[1, 2, 3]
D.
NaN

Question 7.

What does this destructuring assignment do?

const { name, age } = { name: "Alice", age: 25 }; console.log(name, age);

A.
Throws an error
B.
Alice 25
C.
undefined undefined
D.
null null

Question 8.

What will the output be?

const nums = [10, 20, 30]; const doubled = nums.forEach(num => num * 2); console.log(doubled);

A.
[20, 40, 60]
B.
undefined
C.
[10, 20, 30]
D.
An error

Question 9.

What happens if this try-catch block is executed?

try { throw new Error("Something went wrong"); } catch (error) { console.log(error.message); }

A.
Logs "Something went wrong"
B.
Throws an uncaught error
C.
Logs "undefined"
D.
Does nothing

Question 10.

What does this code log?

const greet = (name = "Guest") => `Hello, ${name}!`; console.log(greet());

A.
Hello, !
B.
Hello, Guest!
C.
Hello, undefined!
D.
An error