JavaScript Quiz (Intermediate) - All Questions

This JavaScript Intermediate Quiz is designed for developers who already understand the basics and want to test real-world JavaScript concepts. It covers arrays, objects, functions, scope, DOM manipulation, async behavior, and interview-relevant logic.

Question 1: What is the scope of a variable declared using let?

Global scope
Function scope
Block scope
Module scope

Explanation: Variables declared with let are block-scoped.

Question 2: Which array method returns a new array without modifying the original?

splice()
slice()
push()
pop()

Explanation: slice() returns a shallow copy of an array.

Question 3: What will typeof NaN return?

NaN
undefined
number
object

Explanation: NaN is considered a number type in JavaScript.

Question 4: Which operator checks both value and type equality?

Explanation: === checks both value and data type.

Question 5: Which method converts a NodeList to an array?

Array.from()
toArray()
convert()
map()

Explanation: Array.from() converts iterable objects to arrays.

Question 6: Which keyword prevents reassignment but allows object mutation?

var
let
static
const

Explanation: const prevents reassignment but allows mutation.

Question 7: Which array method is used to transform each element?

filter()
reduce()
map()
find()

Explanation: map() transforms each array element.

Question 8: Which array method returns the first matching element?

filter()
find()
map()
every()

Explanation: find() returns the first matching element.

Question 9: What is the default value of an unassigned function parameter?

null
false
0
undefined

Explanation: Unassigned parameters are undefined.

Question 10: Which method stops event bubbling?

preventDefault()
stop()
stopPropagation()
cancel()

Explanation: stopPropagation() prevents event bubbling.

Question 11: Which keyword refers to the global object in browsers?

document
window
this
global

Explanation: window is the global object in browsers.

Question 12: Which loop is preferred when the number of iterations is unknown?

for
foreach
while
map

Explanation: while loops run based on condition.

Question 13: Which operator spreads array elements?

Explanation: The spread operator expands iterable elements.

Question 14: Which block always executes whether an error occurs or not?

try
catch
throw
finally

Explanation: finally always executes.

Question 15: Which method checks if an array contains a value?

has()
includes()
exists()
contains()

Explanation: includes() checks for value existence.

Question 16: Which function executes code once after a delay?

setInterval()
delay()
setTimeout()
wait()

Explanation: setTimeout() executes code after a delay.

Question 17: Which function executes code repeatedly at intervals?

setTimeout()
repeat()
setInterval()
loop()

Explanation: setInterval() repeats execution.

Question 18: Which method merges two arrays into one?

join()
merge()
concat()
push()

Explanation: concat() merges arrays.

Question 19: Which keyword is used to define a class?

object
function
class
constructor

Explanation: class keyword defines a class.

Question 20: Which method returns all keys of an object?

Object.values()
Object.entries()
Object.keys()
Object.get()

Explanation: Object.keys() returns property names.

Question 21: Which method makes an object immutable?

Object.seal()
Object.freeze()
Object.lock()
const

Explanation: Object.freeze() prevents modifications.

Question 22: Which keyword is used for inheritance in classes?

super
inherits
extends
prototype

Explanation: extends creates inheritance.

Question 23: Which keyword calls the parent class constructor?

this()
parent()
super()
base()

Explanation: super() calls the parent constructor.

Question 24: Which operator handles null or undefined values?

Explanation: Nullish coalescing handles null or undefined.

Question 25: Which method removes whitespace from both ends of a string?

strip()
trim()
clean()
cut()

Explanation: trim() removes leading and trailing spaces.

Question 26: Which keyword exports a module?

send
return
export
share

Explanation: export makes module members available.

Question 27: Which keyword imports a module?

include
require
use
import

Explanation: import loads modules.

Question 28: Which method reduces an array to a single value?

map()
filter()
reduce()
find()

Explanation: reduce() aggregates array values.

Question 29: Which keyword exits a function immediately?

break
stop
exit
return

Explanation: return exits function execution.

Question 30: Which object provides mathematical functions?

Calc
Number
Math
Compute

Explanation: Math provides built-in math utilities.

Question 31: Which method rounds a number down?

Math.round()
Math.ceil()
Math.floor()
Math.fix()

Explanation: Math.floor() rounds down.

Question 32: Which event fires when the DOM is fully loaded?

load
ready
DOMContentLoaded
init

Explanation: DOMContentLoaded fires after DOM parsing.

Question 33: Which method selects all matching elements?

getElementById()
querySelector()
querySelectorAll()
selectAll()

Explanation: querySelectorAll() returns all matching nodes.

Question 34: Which symbol defines an arrow function?

Explanation: => is used in arrow functions.

Question 35: Which feature handles asynchronous operations?

Callbacks
Promises
Async/Await
All of the above

Explanation: All listed options handle async operations.

Question 36: Which Promise state indicates success?

pending
running
fulfilled
rejected

Explanation: fulfilled means the promise resolved.

Question 37: Which keyword pauses execution in async functions?

wait
stop
pause
await

Explanation: await pauses execution until resolved.

Question 38: Which operator checks if a property exists in an object?

has
in
exists
of

Explanation: in checks property existence.

Question 39: Which statement enables strict mode?

use strict
'use strict'
strict()
enableStrict

Explanation: 'use strict' enables strict mode.

Question 40: Which array method tests all elements against a condition?

some()
every()
filter()
find()

Explanation: every() checks all elements.

Question 41: Which array method checks at least one element?

some()
every()
map()
reduce()

Explanation: some() checks at least one element.

Question 42: Which method returns key-value pairs of an object?

Object.keys()
Object.values()
Object.entries()
Object.items()

Explanation: Object.entries() returns key-value pairs.

Question 43: Which operator is used for optional chaining?

Explanation: Optional chaining prevents runtime errors.

Question 44: Which value does a function return by default?

null
false
0
undefined

Explanation: Functions return undefined by default.

Question 45: Which method converts a value to an integer?

Number()
parseInt()
Math.int()
toInt()

Explanation: parseInt() converts to integer.

Question 46: Which keyword defines block-level scope?

var
global
let
scope

Explanation: let is block-scoped.

Question 47: Which operator increments a value by one?

Explanation: ++ increments by one.

Question 48: Which array method removes elements by index?

slice()
pop()
shift()
splice()

Explanation: splice() removes elements by index.

Question 49: Which keyword creates a Promise?

new Promise
Promise()
create Promise
async Promise

Explanation: Promises are created using new Promise().

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JavaScript Quiz (Intermediate)

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JavaScript Quiz (Intermediate)