Here are 20 JavaScript multiple-choice interview questions along with answers:
1. What is the output of the following code?
JavaScript
console.log(typeof null);
- A.
"null" - B.
"object" - C.
"undefined" - D.
"number"
Answer: B. "object"
2. Which of the following is not a primitive data type in JavaScript?
- A. Number
- B. Object
- C. String
- D. Boolean
Answer: B. Object
3. What is the correct syntax to create an array in JavaScript?
- A.
var arr = {}; - B.
var arr = []; - C.
var arr = new Array(); - D. Both B and C
Answer: D. Both B and C
4. Which of the following methods is used to add an element to the end of an array?
- A.
push() - B.
pop() - C.
shift() - D.
unshift()
Answer: A. push()
5. What is the output of the following code?
console.log(2 + "2");
- A.
22 - B.
4 - C.
NaN - D.
Error
Answer: A. 22
6. How do you write an arrow function in JavaScript?
- A.
function => () {} - B.
() => {} - C.
=> function {} - D.
() -> {}
Answer: B. () => {}
7. What will console.log([] == false) output?
- A.
true - B.
false - C.
undefined - D.
Error
Answer: A. true
8. Which keyword is used to declare a constant variable in JavaScript?
- A.
let - B.
var - C.
constant - D.
const
Answer: D. const
9. What is the purpose of isNaN() in JavaScript?
- A. Check if a value is a number
- B. Check if a value is not a number
- C. Check if a value is undefined
- D. Check if a value is null
Answer: B. Check if a value is not a number
10. What does == compare in JavaScript?
- A. Value only
- B. Type only
- C. Value and type
- D. None of the above
Answer: A. Value only
11. Which of the following is used to stop event propagation?
- A.
stopPropagation() - B.
preventDefault() - C.
return false; - D.
clearPropagation()
Answer: A. stopPropagation()
12. What is the purpose of JSON.stringify()?
- A. Convert a JSON string to an object
- B. Convert an object to a JSON string
- C. Parse a URL string
- D. None of the above
Answer: B. Convert an object to a JSON string
13. Which method is used to combine two or more arrays in JavaScript?
- A.
concat() - B.
merge() - C.
join() - D.
add()
Answer: A. concat()
14. What is the output of the following code?
JavaScript
console.log("5" - 2);
- A.
3 - B.
52 - C.
"5-2" - D.
Error
Answer: A. 3
15. Which of the following is a falsy value in JavaScript?
- A.
0 - B.
"" - C.
null - D. All of the above
Answer: D. All of the above
16. What is a closure in JavaScript?
- A. A function inside an object
- B. A function bundled with its lexical environment
- C. A block of code inside curly braces
- D. None of the above
Answer: B. A function bundled with its lexical environment
17. How can you check if a variable is an array?
- A.
typeof variable === "array" - B.
Array.isArray(variable) - C.
variable instanceof Array - D. Both B and C
Answer: D. Both B and C
18. What is the purpose of setTimeout()?
- A. Repeats execution of code at specified intervals
- B. Executes a function after a delay
- C. Stops the execution of code
- D. None of the above
Answer: B. Executes a function after a delay
19. What will console.log(!!"") output?
- A.
true - B.
false - C.
undefined - D.
Error
Answer: B. false
20. Which JavaScript feature allows functions to operate on objects irrespective of their type?
- A. Closures
- B. Prototypes
- C. Polymorphism
- D. Hoisting
Answer: C. Polymorphism
Let me know if you’d like further clarification or more questions!
