JavaScript MCQ

Question :  What is JavaScript primarily used for?

Styling web pages

Server-side scripting

Enhancing user interfaces in web browsers

Database management

Correct Answer : Enhancing user interfaces in web browsers

Question : Which keyword is used to declare a variable in JavaScript?

v

var

variable

int

Correct Answer : var

Question : What will be the result of the following expression: 3 + '3'?

6

'33'

33

Error

Correct Answer : '33'

Question : Which of the following is not a data type in JavaScript?

String

Boolean

Float

Character

Correct Answer : Character

Question : What does the === operator do in JavaScript?

Assignment

Equality (strict comparison)

Inequality

Type coercion

Correct Answer : Equality (strict comparison)

Question : Which function is used to print output in the console in JavaScript?

print()

log()

display()

console()

Correct Answer : log()

Question : What is the purpose of the querySelector method in JavaScript?

Selects the first element that matches a specified CSS selector

Changes the document's URL

Adds a new HTML element

Converts a string to a number

Correct Answer : Selects the first element that matches a specified CSS selector

Question : Which of the following is a loop structure in JavaScript?

repeat

for/in

sequence

until

Correct Answer : for/in

Question : What does the this keyword refer to in JavaScript?

The current file

The calling function

The global object

The previous variable

Correct Answer : The global object

Question : Which event is triggered when a user clicks on an HTML element in JavaScript?

onhover

onsubmit

onclick

onkeydown

Correct Answer : onclick

Question : What is the purpose of the localStorage object in JavaScript?

Storing session-specific data

Storing data locally in the browser

Managing cookies

Accessing the server's file system

Correct Answer : Storing data locally in the browser

Question : Which keyword is used to prevent the execution of code in JavaScript?

prevent

stop

break

debugger

Correct Answer : debugger

Question : What is the result of the following code snippet: console.log(typeof (5 + '5'))?

number

string

NaN

undefined

Correct Answer : string

Question : What is the purpose of the JSON.stringify() method in JavaScript?

Parsing JSON data

Converting a JavaScript object to a JSON string

Retrieving data from an API

Creating a JSON object

Correct Answer : Converting a JavaScript object to a JSON string

Question : Which function is used to create a new element in the DOM in JavaScript?

createElement()

appendChild()

newElement()

addElement()

Correct Answer : createElement()

Question : What is the purpose of the Promise object in JavaScript?

To handle synchronous operations

To represent a value that might be available now, later, or never

To handle errors in asynchronous code

To create anonymous functions

Correct Answer : To represent a value that might be available now, later, or never

Question : What does the typeof operator return for null in JavaScript?

null

object

undefined

number

Correct Answer : object

Question : Which built-in object is used to handle errors in JavaScript?

Error

Exception

ErrorHandler

TryCatch

Correct Answer : Error

Question : What is the purpose of the splice() method in JavaScript?

To remove elements from an array

To add elements to the beginning of an array

To concatenate two arrays

To reverse the order of elements in an array

Correct Answer : To remove elements from an array

Question : Which keyword is used to declare a constant variable in JavaScript?

let

constant

const

var

Correct Answer : const

Question : What is the purpose of the addEventListener method in JavaScript?

To create event listeners for HTML elements

To add attributes to HTML elements

To create new elements in the DOM

To define functions in JavaScript

Correct Answer : To create event listeners for HTML elements

Question : Which of the following statements is true about the 'let' keyword in JavaScript?

It declares a variable with block scope

It declares a variable with function scope

It declares a constant variable

It is used to define a loop

Correct Answer : It declares a variable with block scope

Question : What does the isNaN() function in JavaScript do?

Checks if a value is not a number

Converts a value to a number

Checks if a value is negative

Retrieves the index of an array element

Correct Answer : Checks if a value is not a number

Question : Which of the following is used to iterate over the values of an iterable object in JavaScript?

for loop

forEach loop

while loop

do-while loop

Correct Answer : forEach loop

Question : What does the 'async' keyword do in a function declaration in JavaScript?

Declares a function as asynchronous

Declares a function as anonymous

Defines a function as an arrow function

Indicates a function with a return value

Correct Answer : Declares a function as asynchronous

Question : Which method is used to remove the last element from an array in JavaScript?

pop()

shift()

removeLast()

deleteLast()

Correct Answer : pop()

Question : What is the purpose of the 'bind()' method in JavaScript?

To bind HTML elements to a JavaScript function

To concatenate strings

To bind the value of 'this' in a function

To create a new array

Correct Answer : To bind the value of 'this' in a function

Question : What does the localStorage.removeItem() method do in JavaScript?

Adds a new item to localStorage

Updates an existing item in localStorage

Removes an item from localStorage

Clears all items from localStorage

Correct Answer : Removes an item from localStorage

Question : Which JavaScript method is used to join elements of an array into a string?

concat()

join()

merge()

combine()

Correct Answer : join()

Question : What does the 'arguments' object in a JavaScript function represent?

All parameters passed to the function

The function's return value

The function's local variables

The number of times the function is called

Correct Answer : All parameters passed to the function

Question : Which of the following is true about the 'map()' method in JavaScript?

It modifies the original array

It creates a new array by applying a function to each element

It removes elements from an array

It returns a boolean value

Correct Answer : It creates a new array by applying a function to each element

Question : What is the purpose of the 'typeof' operator in JavaScript?

To check if a variable is defined

To determine the type of a variable

To convert a string to a number

To create a new variable

Correct Answer : To determine the type of a variable

Question : In JavaScript, how do you create a new object using the Object constructor?

var obj = Object.new();

var obj = new Object();

var obj = create Object();

var obj = {}

Correct Answer : var obj = new Object();

Question : What is the purpose of the 'querySelectorAll' method in JavaScript?

Selects the first element that matches a specified CSS selector

Selects all elements that match a specified CSS selector

Removes all elements from the DOM

Adds a new HTML element

Correct Answer : Selects all elements that match a specified CSS selector

Question : Which JavaScript function is used to parse a JSON string?

parseJSON()

stringify()

JSON.parse()

JSON.stringify()

Correct Answer : JSON.parse()

Question : What is the purpose of the 'Object.keys()' method in JavaScript?

Returns an array of an object's enumerable property names

Returns an array of an object's values

Removes all properties from an object

Adds a new property to an object

Correct Answer : Returns an array of an object's enumerable property names

Question : Which statement is used to exit a loop prematurely in JavaScript?

stop

exit

break

end

Correct Answer : break

Question : What is the purpose of the 'Array.isArray()' method in JavaScript?

Checks if an array is empty

Checks if a variable is an array

Adds elements to an array

Concatenates two arrays

Correct Answer : Checks if a variable is an array

Question : Which of the following is not a valid way to declare a function in JavaScript?

function myFunction(){}

const myFunction = function(){}

var myFunction = () => {}

myFunction = function(){}

Correct Answer : myFunction = function(){}

Question : What is the purpose of the 'Array.reduce()' method in JavaScript?

Adds elements to the end of an array

Removes the first element from an array

Applies a function against an accumulator and each element in the array

Reverses the order of elements in an array

Correct Answer : Applies a function against an accumulator and each element in the array