161. What is the output of console.log(1 + +"1")?
- a) 2
- b) "11"
- c) NaN
- d) TypeError
Answer: A - The unary
+ converts "1" to a number, resulting in 1 + 1 = 2.
162. Which method creates a new array with elements that pass a test?
- a) filter()
- b) map()
- c) reduce()
- d) forEach()
Answer: A -
filter() returns a new array with elements that satisfy the condition.
163. What is the output of console.log([] == 0)?
- a) true
- b) false
- c) TypeError
- d) undefined
Answer: A - The empty array
[] is converted to 0 during loose equality comparison.
164. Which method executes a reducer function on each element?
- a) reduce()
- b) map()
- c) filter()
- d) some()
Answer: A -
reduce() accumulates a single result from the array.
165. 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.
166. Which method checks if at least one element passes a test?
- a) some()
- b) every()
- c) includes()
- d) find()
Answer: A -
some() returns true if any element satisfies the condition.
167. What is the output of console.log(typeof NaN)?
- a) "number"
- b) "NaN"
- c) "undefined"
- d) "string"
Answer: A -
NaN is technically of type "number" despite meaning "Not a Number".
168. Which method returns the last index of an element in an array?
- a) lastIndexOf()
- b) findLastIndex()
- c) searchLast()
- d) indexOf() with reverse iteration
Answer: A -
lastIndexOf() searches from the end of the array.
169. What is the output of console.log(+"Infinity")?
- a) Infinity (number type)
- b) "Infinity" (string)
- c) NaN
- d) TypeError
Answer: A - The unary
+ converts the string "Infinity" to the number Infinity.
170. Which method returns the primitive value of an object?
- a) valueOf()
- b) toString()
- c) toPrimitive()
- d) Symbol.toPrimitive
Answer: A -
valueOf() is called when an object needs to be converted to a primitive value.
171. What is the output of console.log(1 == "1")?
- a) true
- b) false
- c) NaN
- d) "11"
Answer: A - Loose equality (
==) performs type coercion, converting the string "1" to the number 1.
172. 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).
173. 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.
174. 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).
175. 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).
176. 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.
177. 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.
178. 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).
179. What is the output of console.log(+"")?
- a) 0
- b) NaN
- c) ""
- d) TypeError
Answer: A - The unary
+ coerces an empty string to 0.
180. 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).