JavaScript Variables: A Comprehensive Guide for Beginners

Question 1

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

Accepted Answer

123abc

Answer

my_variable

Answer

$my-variable

Answer

myVariable

Question 2

What is the data type of the variable 'name' in the following code: var name = 'John'?

Accepted Answer

String

Answer

Number

Answer

Boolean

Answer

Array

Question 3

What is the purpose of using the 'const' keyword when declaring a variable?

Accepted Answer

To create a variable that cannot be reassigned

Answer

To create a variable that is globally accessible

Answer

To declare a variable that can only be used within a specific scope

Answer

To declare a variable that is automatically initialized to a default value

Question 4

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

Accepted Answer

=

Answer

==

Answer

+=

Answer

-=

Question 5

What is the output of the following code: var num = 10; num += 5;

Accepted Answer

15

Answer

5

Answer

10

Answer

undefined

Question 6

What is the key difference between 'let' and 'var' when declaring variables?

Accepted Answer

Let variables are block-scoped, while var variables are function-scoped

Answer

Var variables are block-scoped, while let variables are function-scoped

Answer

Let variables can be reassigned, while var variables cannot

Answer

Var variables can be reassigned, while let variables cannot

Question 7

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

Accepted Answer

Function

Answer

String

Answer

Number

Answer

Boolean

Question 8

What is the purpose of the 'typeof' operator?

Accepted Answer

To determine the data type of a variable

Answer

To convert a variable to a different data type

Answer

To assign a value to a variable

Answer

To compare two variables

Question 9

What is the data type of the variable declared with `let x = 10;`?

Accepted Answer

Number

Answer

Undefined

Answer

String

Answer

Boolean

Question 10

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

Accepted Answer

const PI = 3.14

Answer

PI = 3.14

Answer

var PI = 3.14

Answer

let PI = 3.14

Question 11

Which of the following is the correct syntax to declare a variable in JavaScript?

Accepted Answer

let name = undefined;

Answer

var = name;

Answer

declare name;

Question 12

What is the data type of the following variable: var age = 25;

Accepted Answer

Number

Answer

Boolean

Answer

String

Answer

Object

Question 13

What is the scope of a variable declared with the 'let' keyword?

Accepted Answer

Block

Answer

Class

Answer

Function

Answer

Global

Question 14

What is the purpose of the 'const' keyword when declaring variables?

Accepted Answer

To create a constant variable that cannot be reassigned.

Answer

To create a variable that is only accessible within a specific block.

Answer

To declare a variable that can be accessed from any part of the program.

Question 15

Which of the following is NOT a valid way to declare an array in JavaScript?

Accepted Answer

array = {1, 2, 3};

Answer

array = [1, 2, 3];

Answer

array.push(1, 2, 3);

Answer

array = new Array(1, 2, 3);

Question 16

What is the key difference between primitive and non-primitive data types in JavaScript?

Accepted Answer

Primitive data types are immutable, meaning their value cannot be changed, while non-primitive data types are mutable and can be modified.

Answer

Primitive data types can be assigned to an array, while non-primitive data types cannot.

Answer

Primitive data types are stored in the heap, while non-primitive data types are stored in the stack.

Question 17

Which method can be used to determine the data type of a variable in JavaScript?

Accepted Answer

typeof(variable)

Answer

isType(variable)

Answer

variable.type

Answer

getType(variable)

Question 18

What is the result of the following JavaScript code: var num = 10; num += '5'; console.log(num);

Accepted Answer

105

Answer

NaN

Answer

510

Answer

15

Question 19

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

Accepted Answer

var name;

Answer

define name = 'value';

Answer

name = 'value';

Answer

create name = 'value';

Question 20

Which data type is represented by the following variable value: true?

Accepted Answer

Boolean

Answer

Number

Answer

Undefined

Answer

String

Question 21

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

Accepted Answer

To create a constant variable whose value cannot be changed.

Answer

To declare a variable that can only be used within a specific scope.

Answer

To create a global variable accessible from anywhere in the program.

Question 22

Which JavaScript operator is used for concatenating two strings?

Accepted Answer

+

Answer

/

Answer

*

Answer

%

Question 23

What is the result of the following JavaScript code: var x = 10; x += 5;

Accepted Answer

15

Answer

10

Answer

5

Answer

undefined

Question 24

Which of the following is a valid variable name in JavaScript?

Accepted Answer

name_1

Answer

1name

Answer

name&

Question 25

What is the primary difference between 'let' and 'var' variables in JavaScript?

Accepted Answer

Let variables have block scope, while var variables have function scope.

Answer

Var variables are declared at runtime, while let variables are declared at compile time.

Answer

Let variables cannot be reassigned, while var variables can.

Question 26

Which of the following is NOT a reserved keyword in JavaScript?

Accepted Answer

name

Answer

else

Answer

boolean

Answer

null

Question 27

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

Accepted Answer

To determine the data type of a variable.

Answer

To create a new variable with a different value.

Answer

To check if a variable is defined or not.

Answer

To convert a variable to a different data type.

Question 28

What is the data type of the following variable: const name = 'John'?

Accepted Answer

String

Answer

Object

Answer

Number

Answer

Boolean

Question 29

Which keyword can be used to declare a variable that cannot be reassigned?

Accepted Answer

const

Answer

let

Answer

final

Answer

var

Question 30

Consider the following code: function myFunc() { let x = 10; }. What is the scope of the variable 'x'?

Accepted Answer

Local to the 'myFunc' function

Answer

Accessible from anywhere in the program

Answer

Global

Answer

Block-scoped

Question 31

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

Accepted Answer

=

Answer

:=

Answer

==

Answer

+=

Question 32

What is the data type of a variable declared with the `let` keyword?

Accepted Answer

Mutable

Answer

Undefined

Answer

Constant

Answer

Immutable

Question 33

Which of the following statements correctly declares a global variable in JavaScript?

Accepted Answer

var name = 'John';

Answer

let name = 'John';

Answer

const name = 'John';

Answer

const name;

Question 34

What is the output of the following JavaScript code: `var x = 10; var x = 20; console.log(x);`

Accepted Answer

20

Answer

error

Answer

10

Answer

undefined

Question 35

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

Accepted Answer

1name

Answer

name$

Answer

my-name

Answer

_name

Question 36

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

Accepted Answer

To declare immutable variables.

Answer

To declare mutable variables.

Answer

To declare local variables.

Answer

To declare global variables.

Question 37

Which of the following is an example of a primitive data type in JavaScript?

Accepted Answer

Number

Answer

Object

Answer

Function

Answer

Array

Question 38

Which of the following is a best practice for naming variables in JavaScript?

Accepted Answer

Use descriptive and meaningful names.

Answer

Use Hungarian notation.

Answer

Use random and unique names.

Answer

Use short and cryptic names.

Question 39

What is the purpose of the "const" keyword when declaring a JavaScript variable?

Accepted Answer

To indicate that the variable cannot be reassigned.

Answer

To indicate that the variable is stored in memory.

Answer

To indicate that the variable is global.

Question 40

Which of the following is a valid data type for a JavaScript variable?

Accepted Answer

String

Answer

Int

Answer

Double

Answer

Float

Question 41

What is the difference between a local and a global variable in JavaScript?

Accepted Answer

Local variables are only accessible within the function they are declared in, while global variables can be accessed from anywhere in the program.

Answer

Local variables are stored in memory, while global variables are stored in a stack.

Question 42

Which of the following operators can be used to concatenate two strings in JavaScript?

Accepted Answer

+

Answer

*

Answer

/

Answer

%

Question 43

Which statement correctly declares a variable named 'age' with a value of 25 in JavaScript?

Accepted Answer

let age = 25;

Answer

var age: 25;

Answer

int age = 25;

Answer

age = 25;

Question 44

What is the scope of a variable declared using 'let' in JavaScript?

Accepted Answer

Block scope

Answer

Global scope

Answer

Function scope

Answer

File scope

Question 45

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

Accepted Answer

+

Answer

*

Answer

++

Answer

&

Question 46

Which method can be used to convert a JavaScript string to uppercase?

Accepted Answer

toUpperCase()

Answer

uppercase()

Answer

makeUpperCase()

Answer

string.toUpperCase()

Question 47

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

Accepted Answer

1number

Answer

do_while

Answer

_my_variable

Answer

$dollars

Question 48

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

Accepted Answer

number

Answer

undefined

Answer

boolean

Answer

string

Question 49

Which of the following statements assigns the value 'red' to a variable named 'color' using shorthand notation?

Accepted Answer

color ||= 'red';

Answer

color = 'red';

Answer

color || 'red';

Question 50

Which type of variable can be redeclared with a different value in JavaScript?

Accepted Answer

let

Answer

var

Answer

final

Answer

const

Question 51

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

Accepted Answer

'===' checks for strict equality, while '==' allows type coercion.

Answer

'===' allows type coercion, while '==' checks for strict equality.

Answer

'==' checks for object equality, while '===' checks for value equality.