JavaScript Basics: A Comprehensive Guide for Beginners

Question 1

What is the primary purpose of the 'typeof' operator in JavaScript?

Accepted Answer

To determine the data type of a variable or expression.

Answer

To convert a value to a specific data type.

Answer

To check if a variable is defined.

Question 2

Which operator is used in JavaScript to check the equality of two values?

Accepted Answer

==

Answer

!==

Answer

!=

Answer

=

Question 3

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

Accepted Answer

To declare a variable.

Answer

To define an object.

Answer

To create a function.

Answer

To execute a block of code.

Question 4

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

Accepted Answer

=

Answer

*

Answer

+

Answer

/

Question 5

What is the effect of the following JavaScript code snippet:
var message = 'Hello, world!';

Accepted Answer

Declares the 'message' variable and assigns it the string value 'Hello, world!'.

Answer

Defines an object with a 'message' property.

Answer

Creates a function called 'message'.

Question 6

Which operator in JavaScript is used to test for strict equality between two values?

Accepted Answer

===

Answer

=

Answer

==

Answer

!=

Question 7

What is the functionality of the following JavaScript code block:
if (x > 5) { 
  console.log('x is greater than 5'); 
}

Accepted Answer

Executes the code within the block only if the value of 'x' is greater than 5.

Answer

Defines a function that takes 'x' as an argument.

Answer

Creates an object with a 'console' property.

Question 8

Which of the following syntaxes represents a valid function declaration in JavaScript?

Accepted Answer

function myFunction() {}

Answer

{} function myFunction()

Answer

function myFunction = {}

Answer

myFunction = function() {}

Question 9

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

Accepted Answer

To refer to the current object.

Answer

To call a function.

Answer

To define a variable.

Answer

To return the value of an object.

Question 10

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

Accepted Answer

onlisten

Answer

onclick

Answer

onload

Answer

onmouseover

Question 11

What does the following code do? 
document.getElementById('myElement').style.color = 'red';

Accepted Answer

Changes the color of the HTML element with the id 'myElement' to red

Answer

Gets the element with the id 'myElement' and stores it in a variable

Answer

Adds a CSS class named 'red' to the element with the id 'myElement'

Question 12

Which data type in JavaScript represents a sequence of characters?

Accepted Answer

String

Answer

Boolean

Answer

Array

Answer

Number

Question 13

What is the correct way to declare a variable named 'age' and assign it the value 18 in JavaScript?

Accepted Answer

let age = 18;

Answer

var age = 18;

Answer

age = 18;

Answer

const age = 18;

Question 14

What is the result of the following JavaScript expression: 10 + '5'?

Accepted Answer

105

Answer

15

Answer

NaN

Answer

Error

Question 15

Which operator is used to check if two values are equal in JavaScript?

Accepted Answer

==

Answer

===

Answer

!=

Answer

=

Question 16

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

Accepted Answer

To determine the data type of a value.

Answer

To convert a value to a different data type.

Answer

To check if a value is defined.

Answer

To compare two values.

Question 17

Which of the following is a valid JavaScript comment?

Accepted Answer

// This is a comment

Answer

# This is a comment

Answer

' This is a comment '

Answer

/* This is a comment */

Question 18

What is the output of the following JavaScript code: console.log(5 % 2);?

Accepted Answer

1

Answer

0

Answer

Error

Answer

2.5

Question 19

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

Accepted Answer

'var' allows variable re-declaration, 'let' does not, and 'const' declares a constant.

Answer

'let' is used for block-scoped variables, while 'var' and 'const' have global scope.

Answer

All three keywords declare variables with the same scope and behavior.

Question 20

Which JavaScript operator is used to concatenate strings?

Accepted Answer

+

Answer

*

Answer

/

Answer

-

Question 21

What is the purpose of the 'alert()' function in JavaScript?

Accepted Answer

To display a pop-up message in the browser window.

Answer

To execute a block of code repeatedly.

Answer

To read data from a file.

Answer

To write data to a file.

Question 22

What is the correct way to declare a variable named 'age' and assign it the value 20 in JavaScript?

Accepted Answer

let age = 20;

Answer

age = 20;

Answer

var age = 20;

Question 23

Which data type represents a sequence of characters in JavaScript?

Accepted Answer

String

Answer

Boolean

Answer

Array

Answer

Number

Question 24

What is the result of the following JavaScript expression: 10 + '5'?

Accepted Answer

'105'

Answer

105

Answer

Error

Answer

15

Question 25

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

Accepted Answer

To determine the data type of a variable or expression.

Answer

To perform mathematical calculations.

Answer

To convert a value to a different data type.

Question 26

Which operator is used for modulo (remainder) calculation in JavaScript?

Accepted Answer

%

Answer

/

Answer

**

Answer

*

Question 27

What is the output of the following JavaScript code: console.log(5 > 3);

Accepted Answer

true

Answer

5

Answer

3

Answer

false

Question 28

What is the correct way to write a single-line comment in JavaScript?

Accepted Answer

// This is a comment

Answer

/* This is a comment */

Answer

# This is a comment

Answer

' This is a comment '

Question 29

Which of the following is NOT a valid JavaScript variable name?

Accepted Answer

123abc

Answer

my_variable

Answer

abc123

Answer

myVariable

Question 30

What is the purpose of the 'alert()' function in JavaScript?

Accepted Answer

To display a pop-up message on the webpage.

Answer

To write output to the console.

Answer

To create a new webpage element.

Answer

To read user input from the browser.

Question 31

What is the output of the following JavaScript code: console.log(Math.pow(2, 3));

Accepted Answer

8

Answer

Error

Answer

6

Answer

9