21. What is the output of console.log(1 + "1")?
- a) "11"
- b) 2
- c) NaN
- d) TypeError
Answer: A - JavaScript coerces numbers to strings in string concatenation (
1 becomes "1").
22. Which method flattens a nested array?
- a) flat()
- b) flatten()
- c) join()
- d) concat()
Answer: A -
flat() creates a new array with all sub-array elements concatenated (e.g., [1, [2]].flat() → [1, 2]).
23. What does !!"false" evaluate to?
- a) true
- b) false
- c) "false"
- d) TypeError
Answer: A - The
!! operator converts values to booleans. Non-empty strings are truthy.
24. Which statement about var is true?
- a) It is function-scoped
- b) It is block-scoped
- c) It cannot be reassigned
- d) It hoists to the block level
Answer: A -
var declarations are function-scoped (not block-scoped like let/const).
25. What is the purpose of Object.freeze()?
- a) Prevents modifications to an object
- b) Deep copies an object
- c) Converts an object to JSON
- d) Deletes all object properties
Answer: A -
Object.freeze() makes an object immutable (no additions/deletions/changes).
26. What is the output of console.log(typeof [])?
- a) "object"
- b) "array"
- c) "undefined"
- d) "list"
Answer: A - Arrays are technically objects in JavaScript.
27. Which method converts an object to an array of its values?
- a) Object.values()
- b) Object.keys()
- c) Object.entries()
- d) Array.from()
Answer: A -
Object.values(obj) returns an array of the object's property values.
28. What does setTimeout() return?
- a) A timer ID
- b) A promise
- c) undefined
- d) The callback function
Answer: A -
setTimeout() returns a numeric ID for clearing the timer with clearTimeout().
29. What is the result of Boolean([])?
- a) true
- b) false
- c) []
- d) TypeError
Answer: A - Empty arrays are truthy in JavaScript.
30. Which operator returns the remainder of a division?
- a) %
- b) /
- c) mod
- d) rem
Answer: A - The modulo operator (
%) returns the remainder (e.g., 10 % 3 → 1).
31. What is hoisting in JavaScript?
- a) Moving declarations to the top of their scope
- b) A type of loop
- c) A way to clone objects
- d) An error-handling technique
Answer: A - Hoisting allows variables/functions to be used before declaration (but only declarations are hoisted, not initializations).
32. What is the output of console.log(3 == "3")?
- a) true
- b) false
- c) NaN
- d) TypeError
Answer: A - Loose equality (
==) coerces types, so "3" becomes 3.
33. Which method removes the first element from an array?
- a) shift()
- b) pop()
- c) slice()
- d) unshift()
Answer: A -
shift() removes and returns the first element (mutating the original array).
34. What does Array.isArray([]) return?
- a) true
- b) false
- c) undefined
- d) "array"
Answer: A -
Array.isArray() checks if the argument is an array.
35. What is the default value of an uninitialized variable?
- a) undefined
- b) null
- c) 0
- d) ""
Answer: A - Variables declared but not assigned default to
undefined.
36. Which method merges two or more arrays?
- a) concat()
- b) push()
- c) merge()
- d) join()
Answer: A -
concat() returns a new array combining the originals (e.g., [1].concat([2]) → [1, 2]).
37. What is the output of console.log("5" - 3)?
- a) 2
- b) "53"
- c) NaN
- d) TypeError
Answer: A - The
- operator coerces "5" to a number, resulting in numeric subtraction.
38. Which keyword stops a loop iteration and moves to the next?
- a) continue
- b) break
- c) skip
- d) return
Answer: A -
continue skips the current iteration and proceeds to the next.
39. What is the output of console.log(+"10")?
- a) 10
- b) "10"
- c) NaN
- d) TypeError
Answer: A - The unary
+ operator converts strings to numbers.
40. Which method checks if an array includes a value?
- a) includes()
- b) contains()
- c) indexOf()
- d) find()
Answer: A -
includes() returns true if the value exists in the array.