JavaScript Basics: Master the Fundamentals of Web Development

Question 1

What is the output of the following JavaScript code: console.log(typeof 'Hello');

Accepted Answer

String

Answer

Number

Answer

Boolean

Answer

Object

Question 2

What is the purpose of the 'this' keyword in JavaScript?

Accepted Answer

References the current object

Answer

References the global object

Answer

References the parent object

Answer

References the child object

Question 3

What is the purpose of the 'document' object in JavaScript?

Accepted Answer

Provides access to the HTML document

Answer

Provides access to the CSS stylesheet

Answer

Provides access to the browser window

Answer

Provides access to the server

Question 4

What is the output of the following JavaScript code: console.log(Math.max(10, 20, 30));

Accepted Answer

30

Answer

10

Answer

20

Answer

undefined

Question 5

Which JavaScript operator is used to assign a value to a variable?

Accepted Answer

=

Answer

+

Answer

:

Answer

=>

Question 6

In JavaScript, which of these are considered valid data types?

Accepted Answer

Integer

Accepted Answer

Double

Accepted Answer

String

Answer

Character

Question 7

In JavaScript, which syntax is correct for declaring a variable?

Accepted Answer

var x;

Answer

x = ;

Answer

int x;

Answer

double x;

Question 8

What is the primary purpose of the 'console.log()' function in JavaScript?

Accepted Answer

To display output on the user's console

Answer

To save data to a file

Answer

To format input data

Answer

To manipulate DOM elements

Question 9

Which syntax is correct for declaring a function in JavaScript?

Accepted Answer

function myFunction(params) {}

Answer

myFunction(params) {}

Answer

define myFunction(params) {}

Answer

function = myFunction(params) {}

Question 10

What is the difference between the == and === operators in JavaScript?

Accepted Answer

== checks for value equality, === checks for value and type equality

Answer

== checks for type equality, === checks for value equality

Answer

Both operators perform the same comparison

Answer

== is used for object comparison, === is used for primitive value comparison

Question 11

What is the output of the following JavaScript code: console.log(typeof null);?

Accepted Answer

object

Answer

null

Answer

undefined

Answer

Error

Question 12

What is the function of the 'break' statement in a JavaScript switch statement?

Accepted Answer

To terminate execution of the switch statement and exit the switch block

Answer

To terminate execution of the switch statement and fall through to the next case

Answer

To skip execution of the current case and continue to the next case

Answer

There is no 'break' statement in a JavaScript switch statement

Question 13

Precisely, what is the syntax to add a CSS class to an HTML element using JavaScript's DOM manipulation?

Accepted Answer

element.classList.add('myClass')

Answer

element.addClass('myClass')

Answer

element.setAttribute('class', 'myClass')

Answer

element.className += 'myClass'

Question 14

Identify the valid JavaScript conditional statement among the choices:

Accepted Answer

if (condition)

Answer

if condition:

Answer

if condition == true

Answer

if (condition) then

Question 15

What outcome is produced by the following JavaScript code?
console.log(typeof 10 + '5');

Accepted Answer

'105'

Answer

105

Answer

15

Answer

undefined

Question 16

In JavaScript, what is the primary purpose of the 'document' object?

Accepted Answer

HTML Document Representation

Answer

Creating New HTML Elements

Answer

Handling Events

Answer

Making Ajax Requests

Question 17

In JavaScript, what is the function of the 'getElementById()' method?

Accepted Answer

Select an HTML Element by its ID

Answer

Create a New HTML Element

Answer

Add an Event Listener to an HTML Element

Answer

Get the Current Mouse Position

Question 18

What is the primary purpose of using the 'this' keyword in JavaScript?

Accepted Answer

To refer to the current object

Answer

To create a new object

Answer

To invoke a method

Answer

To define a variable

Question 19

What is the primary use case of the 'debugger' statement in JavaScript?

Accepted Answer

To halt execution and enter the debugging console

Answer

To log a message to the console

Answer

To set a breakpoint

Answer

To throw an error

Question 20

Which JavaScript operator is used to concatenate two or more strings?

Accepted Answer

+

Answer

-

Answer

*

Answer

%

Question 21

What is the default value assigned to a JavaScript variable that has not been explicitly initialized?

Accepted Answer

undefined

Answer

0

Answer

null

Answer

false

Question 22

What is the primary purpose of the 'document.getElementById' method in JavaScript?

Accepted Answer

To retrieve an element from the HTML document based on its unique ID

Answer

To create a new element in the HTML document

Answer

To remove an element from the HTML document

Answer

To modify the style of an element in the HTML document

Question 23

What is the primary purpose of the 'setTimeout' function in JavaScript?

Accepted Answer

To execute a function after a specified delay in milliseconds

Answer

To execute a function repeatedly at a specified interval

Answer

To stop the execution of a function

Answer

To pause the execution of a function

Question 24

Which of the following correctly describes the behavior of the '==' operator in JavaScript?

Accepted Answer

Checks for value equality, regardless of data type

Answer

Checks for value and type equality

Answer

Assigns a value to a variable

Answer

Compares two objects for reference equality

Question 25

What is the purpose of the Document Object Model (DOM) in web development?

Accepted Answer

Provides a hierarchical representation of an HTML or XML document

Answer

Defines the structure and appearance of a web page

Answer

Handles user interaction and events

Answer

Stores data for a web application

Question 26

Which JavaScript method is used to add an event listener to an HTML element?

Accepted Answer

addEventListener

Answer

attachListener

Answer

listenForEvent

Answer

registerEventHandler

Question 27

What is the difference between 'let' and 'const' variable declarations in JavaScript?

Accepted Answer

Let allows reassignment while const does not

Answer

Const allows reassignment while let does not

Answer

Let has block scope while const has global scope

Answer

They are the same

Question 28

What is the purpose of the 'async' keyword in JavaScript?

Accepted Answer

Allows asynchronous operations without blocking the main thread

Answer

Prevents asynchronous operations from running

Answer

Makes a function synchronous

Answer

Handles errors in asynchronous operations

Question 29

What is the primary purpose of using 'strict mode' in JavaScript?

Accepted Answer

Enforces stricter syntax and error handling

Answer

Improves performance

Answer

Reduces memory usage

Question 30

What is the primary purpose of the 'async' keyword in JavaScript?

Accepted Answer

Allows functions to execute asynchronously, without blocking the main thread

Answer

Improves performance

Answer

Reduces memory usage

Question 31

Which of the following is NOT a valid primitive data type in JavaScript?

Accepted Answer

Void

Answer

Number

Answer

String

Answer

Boolean

Question 32

What is the primary purpose of the 'this' keyword in JavaScript?

Accepted Answer

To refer to the current object within a method or function

Answer

To refer to the global object

Answer

To refer to the parent object

Answer

To refer to the child object

Question 33

Which control flow statement is used to execute a block of code repeatedly as long as a condition is true?

Accepted Answer

while

Answer

if

Answer

switch

Answer

for

Question 34

Which function is used to create a new JavaScript object using the object-literal syntax?

Accepted Answer

new Object()

Answer

object()

Answer

create()

Answer

make()

Question 35

What is the primary purpose of using 'strict mode' in JavaScript?

Accepted Answer

To enforce stricter coding rules and prevent bad coding practices

Answer

To loosen coding rules and allow more flexibility

Answer

To enable access to new features

Answer

To disable old features

Question 36

Which event listener is used to detect when a user clicks on an element in the DOM?

Accepted Answer

onclick

Answer

onmouseover

Answer

onchange

Answer

onkeydown

Question 37

Which JavaScript method is used to convert a string to uppercase?

Accepted Answer

toUpperCase()

Answer

toUpper()

Answer

upper()

Answer

toUpperCaseString()

Question 38

What is the difference between var, let, and const in JavaScript?

Accepted Answer

Var is global, let is block-scoped, const is immutable

Answer

Var is block-scoped, let is global, const is immutable

Answer

Var is immutable, let is global, const is block-scoped

Answer

Var is block-scoped, let is immutable, const is global

Question 39

What is the purpose of the 'var' keyword in JavaScript?

Accepted Answer

To define a variable

Answer

To declare a function

Answer

To create an object

Answer

To initialize an array

Question 40

Which of the following operators is used for logical AND in JavaScript?

Accepted Answer

&&

Answer

||

Answer

&

Answer

|

Question 41

What is the purpose of the 'let' keyword in JavaScript?

Accepted Answer

Declares a block-scoped variable

Answer

Declares a constant variable

Answer

Declares a global variable

Answer

Initializes an array

Question 42

Which of the following operators is used for assignment in JavaScript?

Accepted Answer

=

Answer

==

Answer

+=

Answer

*=

Question 43

What is the primary purpose of the 'getElementById()' method in JavaScript?

Accepted Answer

Retrieves an element from the DOM based on its unique ID

Answer

Creates a new element in the DOM

Answer

Modifies the style of an existing element

Answer

Removes an element from the DOM

Question 44

Which event listener is triggered when a user clicks on an HTML element?

Accepted Answer

'click'

Answer

'change'

Answer

'submit'

Answer

'load'

Question 45

What is the correct syntax for creating an array in JavaScript?

Accepted Answer

[]

Answer

{}

Answer

()

Answer

''

Question 46

What is the main purpose of the 'document.querySelector()' method in JavaScript?

Accepted Answer

Selects the first element that matches a specified CSS selector within the document

Answer

Selects all elements that match a specified CSS selector within the document

Answer

Creates a new element in the DOM

Answer

Removes an element from the DOM

Question 47

In JavaScript, functions are first-class. What does this mean and how can you use this feature?

Accepted Answer

Functions can be assigned to variables, passed as arguments, and returned from other functions.

Answer

Functions cannot be modified once created.

Answer

Functions can only be executed within the global scope.

Question 48

What is the correct syntax to declare a constant variable in JavaScript?

Accepted Answer

const myVariable = 'value';

Answer

var myVariable: 'value';

Answer

let myVariable == 'value';

Answer

myVariable = 'value';

Question 49

What is the JavaScript data type of the variable in the following code: `let age = 25;`?

Accepted Answer

Number

Answer

String

Answer

Boolean

Answer

Object

Question 50

What is the result of the following JavaScript expression: `10 % 3;`?

Accepted Answer

1

Answer

0

Answer

3

Answer

10

Question 51

Which event listener is used to respond to a mouse click event?

Accepted Answer

onclick

Answer

onhover

Answer

onenter

Answer

onload

Question 52

What does the `document.querySelector()` method do?

Accepted Answer

Selects the first element that matches a specified CSS selector

Answer

Selects all elements that match a specified CSS selector

Answer

Creates a new element in the DOM

Answer

Removes an element from the DOM

Question 53

Which of the following statements accurately describes the difference between an inner function and a closure in JavaScript?

Accepted Answer

An inner function is a type of closure, but a closure is not necessarily an inner function.

Answer

An inner function cannot access variables outside its scope, while a closure can.

Answer

A closure cannot access variables outside its scope, while an inner function can.

Answer

There is no difference between an inner function and a closure in JavaScript.

Question 54

What is the primary purpose of a Content Delivery Network (CDN) in JavaScript web development?

Accepted Answer

To enhance the performance of web applications by delivering content from geographically distributed servers

Answer

To provide security for web applications

Answer

To manage user sessions

Answer

To store user data

Question 55

What is the function of the 'var' keyword in JavaScript?

Accepted Answer

To declare a variable

Answer

To define a function

Answer

To create an object

Answer

To execute a conditional statement

Question 56

To select a single HTML element by its CSS selector, which JavaScript method should you use?

Accepted Answer

document.querySelector()

Answer

document.getElementById()

Answer

document.getElementsByClassName()

Answer

document.getElementsByName()

Question 57

Which event listener is used to handle user clicks on an HTML element?

Accepted Answer

onclick

Answer

onload

Answer

onmouseover

Answer

onchange

Question 58

What is the key difference between 'let' and 'const' variable declarations in JavaScript?

Accepted Answer

'Let' variables are mutable while 'const' variables are immutable

Answer

'Const' variables are mutable while 'let' variables are immutable

Answer

There is no difference between 'let' and 'const' variables

Answer

'Let' variables have block scope while 'const' variables have global scope

Question 59

To prevent the default behavior of an event in JavaScript, which method can be utilized?

Accepted Answer

preventDefault()

Answer

stopPropagation()

Answer

addDefaultListener()

Answer

createEvent()

Question 60

What data type is represented by the following value: 'Hello World'?

Accepted Answer

String

Answer

Number

Answer

Boolean

Answer

Array

Question 61

Which operator in JavaScript represents logical conjunction?

Accepted Answer

&&

Answer

||

Answer

!

Answer

==

Question 62

What is the purpose of the 'document.querySelector()' method?

Accepted Answer

Selects the first element that matches a specified CSS selector

Answer

Creates a new element

Answer

Removes an element from the DOM

Answer

Modifies the style of an element

Question 63

What is the correct syntax for defining a function in JavaScript using arrow functions?

Accepted Answer

<function_name>(<parameters>) => {}

Answer

function <function_name>() {}

Answer

function () {}

Answer

<function_name>() => {}

Question 64

Which of the following describes a key advantage of using JavaScript in web development?

Accepted Answer

Enabling the creation of dynamic and interactive user interfaces

Answer

Improving website performance and responsiveness

Answer

Enhancing website security and protecting sensitive data

Answer

Simplifying server-side programming, reducing the need for complex back-end code