JavaScript Programming: Master the Fundamentals for Web Development

Question 1

Which JavaScript data type is used exclusively for representing true or false values?

Accepted Answer

Boolean

Answer

Number

Answer

String

Answer

Array

Question 2

Which of these is **not** a primitive data type in JavaScript?

Accepted Answer

Object

Answer

Number

Answer

Boolean

Answer

String

Question 3

Which syntax is correct for declaring a variable named 'name' with a value of 'John' in JavaScript?

Accepted Answer

let name = 'John';

Answer

name = 'John';

Answer

const name: 'John';

Answer

var John = 'name';

Question 4

Which of the following operators has the highest precedence in JavaScript?

Accepted Answer

Parentheses ()

Answer

Strict equality (===)

Answer

Logical AND (&&)

Answer

Addition (+)

Question 5

What is the purpose of the following function: function add(a, b) { return a + b; } in JavaScript?

Accepted Answer

Adds two numbers and returns the result

Answer

Creates a new object

Answer

Compares two strings

Answer

Manipulates the DOM

Question 6

Which of the following is the correct syntax for creating an array in JavaScript that contains the elements 1, 2, and 3?

Accepted Answer

[1, 2, 3]

Answer

{1, 2, 3}

Answer

(1, 2, 3)

Answer

1, 2, 3

Question 7

In JavaScript, what is the primary purpose of the 'this' keyword?

Accepted Answer

Refers to the object that owns the currently executing code

Answer

Declares a global variable

Answer

Can be used as a function parameter

Answer

Stores the value of the last executed function

Question 8

Which of the following DOM events is triggered when the user clicks on an element?

Accepted Answer

"onclick"

Answer

"onhover"

Answer

"onblur"

Answer

"onchange"

Question 9

Explain the difference between the '==' and '===' operators in JavaScript

Accepted Answer

'=' checks for loose equality (value equality) while '===' checks for strict equality (value and type equality)

Answer

'===' is for objects, '==' is for primitives

Answer

'==' is for numbers, '===' is for strings

Question 10

What will be the output of the following code in JavaScript: var x = 5; var y = '5'; console.log(x === y);

Accepted Answer

false

Answer

true

Answer

5

Answer

undefined

Question 11

Which of these options represents a valid syntax for defining a class named 'MyClass' in JavaScript?

Accepted Answer

class MyClass {}

Answer

const MyClass = {}

Answer

var MyClass = {}

Answer

function MyClass {}

Question 12

Which of the following is the correct syntax for declaring a constant variable in JavaScript?

Accepted Answer

const PI = 3.14;

Answer

var PI = 3.14;

Answer

PI = 3.14

Answer

let PI = 3.14

Question 13

Which of the following is the correct syntax for a while loop in JavaScript?

Accepted Answer

while (condition) {}

Answer

foreach (i in 10) {}

Answer

do { } while (condition);

Answer

for (let i = 0; i < 10; i++) {}

Question 14

What is the purpose of the JavaScript document.querySelectorAll() method?

Accepted Answer

Selects a list of elements that match a specified CSS selector.

Answer

Gets or sets the content of an element.

Answer

Creates a new HTML element.

Answer

Attaches an event listener to an element.

Question 15

Which of the following is a commonly used HTTP method for retrieving data from a web server?

Accepted Answer

GET

Answer

PUT

Answer

DELETE

Answer

POST

Question 16

What is the role of the JavaScript event.stopPropagation() method?

Accepted Answer

Stops the propagation of an event to its parent elements.

Answer

Attaches an event listener to an element.

Answer

Triggers an event.

Answer

Prevents the default behavior of an event.

Question 17

Which of the following is a valid JavaScript array method for removing the first element from an array?

Accepted Answer

shift()

Answer

delete()

Answer

remove()

Answer

pop()

Question 18

What is the purpose of the window.onunload event in JavaScript?

Accepted Answer

Executes a script when the user is about to leave the page.

Answer

Attaches an event listener to the window object.

Answer

Triggers when the user scrolls down the page.

Answer

Initializes the JavaScript environment.

Question 19

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

Accepted Answer

Object

Answer

Number

Answer

Boolean

Answer

String

Question 20

What operator is used to assign a value to a variable in JavaScript?

Accepted Answer

=

Answer

*

Answer

+

Answer

-

Question 21

What is the syntax to declare a function in JavaScript?

Accepted Answer

function functionName() { ... }

Answer

new functionName() { ... }

Answer

define functionName() { ... }

Answer

create functionName() { ... }

Question 22

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

Accepted Answer

References the current object.

Answer

Stores the value of the previous expression.

Answer

Defines a global variable.

Question 23

Which of the following is a valid way to define an array in JavaScript?

Accepted Answer

[]

Answer

()

Answer

<>

Answer

{}

Question 24

What method is used to add an element to the end of an array in JavaScript?

Accepted Answer

push()

Answer

insert()

Answer

append()

Answer

add()

Question 25

Which of the following loops is used to iterate over each element of an array in JavaScript?

Accepted Answer

for...of

Answer

for...in

Answer

while

Answer

do...while

Question 26

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

Accepted Answer

`===` checks for strict equality (value and type), while `==` performs type coercion.

Answer

`==` checks for strict equality, while `===` performs type coercion.

Answer

`===` is only used for numbers, while `==` can be used for all data types.

Question 27

How do you access the properties of an object in JavaScript?

Accepted Answer

Dot notation or square brackets

Answer

Semicolons

Answer

Curly braces

Answer

Parentheses

Question 28

Which of the following is an event listener in JavaScript?

Accepted Answer

addEventListener()

Answer

listenTo()

Answer

onEvent()

Answer

triggerEvent()

Question 29

Which of the following operators is used to compare two values for strict equality in JavaScript?

Accepted Answer

===

Answer

!=

Answer

>=

Answer

==

Question 30

What is the primary purpose of a function in JavaScript?

Accepted Answer

To encapsulate code that performs a specific task and can be reused as needed.

Answer

To store data permanently in memory.

Answer

To execute code only once.

Question 31

Which JavaScript method is used to select an HTML element by its unique ID?

Accepted Answer

getElementById

Answer

querySelector

Answer

getElementByName

Answer

getElementByClass

Question 32

What is the purpose of the 'addEventListener' method in JavaScript?

Accepted Answer

To attach an event listener to an HTML element and wait for a specific event to occur.

Answer

To send data to a server.

Answer

To create a new HTML element.

Answer

To modify the CSS style of an element.

Question 33

What is the output of the following JavaScript code: const arr = [1, 2, 3]; arr.push(4); console.log(arr.length);

Accepted Answer

4

Answer

undefined

Answer

3

Answer

[1, 2, 3, 4]

Question 34

Which of the following operators is used to compare two values for strict equality in JavaScript?

Accepted Answer

===

Answer

!=

Answer

=

Answer

==

Question 35

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

Accepted Answer

To declare a reusable block of code that can be invoked when needed.

Answer

To declare a variable.

Answer

To create an object.

Answer

To perform a mathematical operation.

Question 36

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

Accepted Answer

'let' declares a variable that can be reassigned, while 'const' declares a constant that cannot be changed.

Answer

'let' is used for global variables, while 'const' is used for local variables.

Question 37

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

Accepted Answer

To reference the current object within a method or function.

Answer

To reference the child object.

Answer

To reference the global object.

Answer

To reference the parent object.

Question 38

Which of the following methods is used to add an element to the end of an array in JavaScript?

Accepted Answer

push()

Answer

shift()

Answer

pop()

Question 39

What is the difference between 'document.getElementById()' and 'document.getElementsByClassName()' in JavaScript?

Accepted Answer

'getElementById()' retrieves an element by its unique ID, while 'getElementsByClassName()' retrieves a list of elements with the specified class name.

Answer

'getElementById()' retrieves an element by its class name, while 'getElementsByClassName()' retrieves an element by its ID.

Question 40

Which of the following event listeners is used to handle mouse clicks in JavaScript?

Accepted Answer

click

Answer

keypress

Answer

mousemove

Answer

hover

Question 41

Which data type holds sequences of characters?

Accepted Answer

String

Answer

Number

Answer

Array

Answer

Boolean

Question 42

Which operator is used to concatenate strings?

Accepted Answer

+

Answer

%

Answer

/

Answer

*

Question 43

Which method adds a new element to an array's end?

Accepted Answer

push()

Answer

insert()

Answer

add()

Answer

append()

Question 44

Which method creates an event listener in JavaScript?

Accepted Answer

element.addEventListener('event', function) {}

Answer

element.listen('event', function) {}

Answer

element.on('event', function) {}

Answer

element.attachEvent('event', function) {}

Question 45

Which built-in function delays an action in JavaScript?

Accepted Answer

setTimeout()

Answer

wait()

Answer

delay()

Answer

pause()

Question 46

Which technique encapsulates data and behavior in JavaScript?

Accepted Answer

Object-oriented programming

Answer

Procedural programming

Answer

Event-driven programming

Answer

Functional programming

Question 47

In JavaScript, which keyword is used to declare a variable?

Accepted Answer

var

Answer

variable

Answer

int

Answer

string

Question 48

What data type does the JavaScript expression `typeof "5"` return?

Accepted Answer

string

Answer

undefined

Answer

boolean

Answer

number

Question 49

Which operator is used for string concatenation in JavaScript?

Accepted Answer

+

Answer

*

Answer

-

Answer

&

Question 50

What is the correct syntax for an IF statement in JavaScript?

Accepted Answer

if (condition) { // code }

Answer

if condition { // code }

Answer

check condition { // code }

Answer

if (condition); { // code }

Question 51

What is the primary function of the `return` keyword within a JavaScript function?

Accepted Answer

To specify the value returned by the function.

Answer

To exit the entire program immediately.

Answer

To define a new variable within the function.

Answer

To print the function's output to the console.

Question 52

Which built-in function is used to display a message in the browser's console?

Accepted Answer

console.log()

Answer

write()

Answer

output()

Answer

print()

Question 53

What is the purpose of an array in JavaScript?

Accepted Answer

To store a collection of data items under a single variable.

Answer

To perform mathematical operations on numbers.

Answer

To define custom data types.

Question 54

What is a callback function in JavaScript?

Accepted Answer

A function passed as an argument to another function, to be executed later.

Answer

A function that calls itself repeatedly.

Answer

A function that returns another function.