141. What is the output of console.log(+"0x10")?
- a) 16
- b) "0x10"
- c) 10
- d) NaN
Answer: A - The unary
+ converts hexadecimal "0x10" to decimal 16.
142. Which method creates a new array with the results of calling a function on every element?
- a) map()
- b) forEach()
- c) filter()
- d) reduce()
Answer: A -
map() transforms each element and returns a new array.
143. What is the output of console.log(typeof (() => {}))?
- a) "function"
- b) "object"
- c) "arrow"
- d) "undefined"
Answer: A - Arrow functions are still of type
"function".
144. 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).
145. What is the output of console.log(0 || "Hello")?
- a) "Hello"
- b) 0
- c) true
- d) false
Answer: A - The logical OR (
||) returns the first truthy value ("Hello" in this case).
146. 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.
147. What is the output of console.log(+"")?
- a) 0
- b) NaN
- c) ""
- d) TypeError
Answer: A - The unary
+ coerces an empty string to 0.
148. Which method returns the first element that satisfies a condition?
- a) find()
- b) filter()
- c) some()
- d) indexOf()
Answer: A -
find() returns the first matching element (or undefined if none).
149. What is the output of console.log(3 > 2 > 1)?
- a) false
- b) true
- c) TypeError
- d) undefined
Answer: A - Evaluated as
(3 > 2) > 1 → true > 1 → 1 > 1 → false.
150. Which symbol is used as a placeholder for awaiting promises?
- a) await
- b) async
- c) then
- d) yield
Answer: A -
await pauses execution until a promise settles (must be inside an async function).
151. What is the output of console.log(Number("123abc"))?
- a) NaN
- b) 123
- c) "123abc"
- d) TypeError
Answer: A -
Number() returns NaN for strings with non-numeric characters.
152. Which method returns a string representation of an array?
- a) toString()
- b) join()
- c) String()
- d) All of the above
Answer: D - All three methods convert arrays to strings, but
join() allows custom separators.
153. What is the output of console.log(typeof class {})?
- a) "function"
- b) "class"
- c) "object"
- d) "undefined"
Answer: A - Classes are syntactic sugar over constructor functions, so their type is
"function".
154. Which method prevents extensions to an object?
- a) Object.preventExtensions()
- b) Object.seal()
- c) Object.freeze()
- d) All of the above
Answer: A -
Object.preventExtensions() disables adding new properties (but allows modifying/deleting existing ones).
155. What is the output of console.log(!!new Boolean(false))?
- a) true
- b) false
- c) "false"
- d) TypeError
Answer: A -
new Boolean(false) is an object (truthy), so !! converts it to true.
156. Which operator has the highest precedence?
- a) () (grouping)
- b) . (member access)
- c) new (with argument list)
- d) ++ (postfix increment)
Answer: A - Grouping
() has the highest precedence, followed by member access . and new.
157. What does console.log(new String("test") === "test") output?
- a) false
- b) true
- c) TypeError
- d) undefined
Answer: A - The
String object and primitive string are of different types (object vs string).
158. Which method creates a new array with all sub-array elements concatenated recursively?
- a) flat()
- b) flatMap()
- c) concat()
- d) join()
Answer: A -
flat(depth) flattens nested arrays up to the specified depth (default: 1).
159. What is the output of console.log(typeof (function(){}()))?
- a) "undefined"
- b) "function"
- c) "object"
- d) "null"
Answer: A - The IIFE (Immediately Invoked Function Expression) returns nothing, so its type is
undefined.
160. Which statement about let and const is true?
- a) Both are block-scoped
- b) Both are hoisted to the function scope
- c)
constallows reassignment - d)
letdoesn't support temporal dead zone
Answer: A -
let and const are block-scoped and hoisted but cannot be accessed before declaration (temporal dead zone).