JavaScript Programming: Master the Fundamentals for Web Development

Question 1

Which of the following is a valid JavaScript variable name?

Accepted Answer

_myVariable (underscore followed by letters)

Answer

my-variable (hyphen is not allowed)

Answer

123variable (cannot start with a number)

Answer

var my_variable (cannot use the reserved keyword 'var')

Question 2

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

Accepted Answer

To declare a constant variable (cannot be reassigned)

Answer

To create a new object (not its purpose)

Answer

To define a function (not its purpose)

Answer

To loop through an array (not its purpose)

Question 3

Which of the following is an example of a JavaScript operator?

Accepted Answer

+ (addition operator)

Answer

if (conditional statement, not an operator)

Answer

function (used to define functions)

Answer

console.log (used for debugging, not an operator)

Question 4

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

Accepted Answer

===' checks for strict equality, while '==' checks for loose equality

Answer

There is no difference between '===' and '==' (incorrect)

Answer

===' is used for numbers, while '==' is used for strings (incorrect)

Answer

===' is used for objects, while '==' is used for arrays (incorrect)

Question 5

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

Accepted Answer

To get an element by its ID

Answer

To create a new element (not its purpose)

Answer

To add an event listener to an element (not its purpose)

Answer

To remove an element from the DOM (not its purpose)

Question 6

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

Accepted Answer

To make a function asynchronous (can be paused and resumed)

Answer

To create a new thread (not its purpose)

Answer

To make a function parallel (not its purpose)

Answer

To wait for a promise to resolve (not its direct purpose)

Question 7

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

Accepted Answer

'==' checks for value equality, while '===' checks for both value and type equality

Answer

'==' checks for type equality, while '===' checks for value equality

Answer

They are equivalent and can be used interchangeably

Answer

There is no difference between them

Question 8

Which of the following JavaScript array methods is used to remove the last element from the array?

Accepted Answer

pop()

Answer

remove()

Answer

delete()

Answer

shift()

Question 9

What is the purpose of using a 'try-catch' block in JavaScript?

Accepted Answer

To handle potential errors and provide a fallback mechanism

Answer

To improve code organization

Answer

To prevent the execution of specific code blocks

Answer

To debug JavaScript code

Question 10

Which of the following is NOT a valid JavaScript event listener?

Accepted Answer

onhover

Answer

onclick

Answer

onkeydown

Answer

onload

Question 11

What is the DOM (Document Object Model) in JavaScript?

Accepted Answer

A hierarchical representation of the HTML document, allowing for dynamic manipulation

Answer

A database that stores website data

Answer

A programming language used to create websites

Answer

A tool for managing user interactions

Question 12

In JavaScript, explain the significance and context-dependent nature of the 'this' keyword.

Accepted Answer

'This' refers to the current object within its context, making it a dynamic keyword.

Answer

'This' always points to the global object, regardless of the function's context.

Answer

'This' is only relevant in object-oriented programming, not in functional programming.

Question 13

What's the primary benefit of using strict mode in JavaScript?

Accepted Answer

Prevents silent errors by triggering exceptions during development.

Answer

Enhances code performance.

Answer

Improves code readability.

Answer

Enforces type checking.

Question 14

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

Accepted Answer

Variable

Answer

String

Answer

Number

Answer

Boolean

Question 15

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

Accepted Answer

To declare a variable with block scope

Answer

To declare a constant variable

Answer

To declare a global variable

Answer

To declare an anonymous function

Question 16

Which control flow statement is used to repeatedly execute a block of code until a condition is met?

Accepted Answer

while

Answer

if-else

Answer

switch

Answer

for

Question 17

What is the correct syntax to define a function in JavaScript?

Accepted Answer

function myFunction(params) { ... }

Answer

myFunction(params) { ... }

Answer

function: myFunction(params) { ... }

Answer

def myFunction(params): { ... }

Question 18

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

Accepted Answer

arr[index]

Answer

arr.index

Answer

get(arr, index)

Answer

arr->index

Question 19

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

Accepted Answer

To refer to the current object

Answer

To refer to the global object

Answer

To refer to the parent object

Answer

To refer to the function object

Question 20

Which event listener is used to detect when the mouse is clicked on an HTML element?

Accepted Answer

onclick

Answer

onmouseover

Answer

onkeydown

Answer

onchange

Question 21

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

Accepted Answer

To represent the HTML document

Answer

To represent the CSS stylesheet

Answer

To represent the JavaScript code

Answer

To represent the DOM

Question 22

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

Accepted Answer

Timestamp

Answer

Boolean

Answer

Number

Answer

String

Question 23

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

Accepted Answer

To refer to the current object's context

Answer

To create a new JavaScript object

Answer

To define a global variable

Answer

To call a function from another object

Question 24

Which control flow statement is used to repeatedly execute a block of code while a specified condition remains true?

Accepted Answer

while

Answer

switch

Answer

if-else

Answer

for

Question 25

What is the correct syntax to define a function in JavaScript?

Accepted Answer

function functionName(parameters) { code block }

Answer

function() functionName(parameters) { code block }

Answer

define function functionName(parameters) { code block }

Answer

functionName(parameters) { code block }

Question 26

Which of the following is a valid event handler for responding to a user clicking an HTML element?

Accepted Answer

onclick

Answer

onchange

Answer

onsubmit

Answer

onhover

Question 27

What is the expected output of the following JavaScript expression in the console: console.log(typeof(null));

Accepted Answer

object

Answer

undefined

Answer

boolean

Answer

null

Question 28

Which operator should be used to concatenate two strings in JavaScript?

Accepted Answer

+

Answer

&

Answer

*

Question 29

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

Accepted Answer

To select and return an HTML element based on its unique ID

Answer

To create a new HTML element

Answer

To remove an HTML element

Answer

To modify the style of an HTML element

Question 30

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

Accepted Answer

'Let' variables can be reassigned, while 'const' variables cannot.

Answer

'Const' variables can be reassigned, while 'let' variables cannot.

Answer

Neither 'let' nor 'const' variables can be reassigned.

Answer

Both 'let' and 'const' variables can be reassigned.