JavaScript Variables Quiz - Multiple Choice Questions (MCQ)

Welcome to the JavaScript quiz on Variables. This quiz consists of 10+ multiple-choice questions, answers, and explanations. Let's dive into the world of JavaScript Variables and put your skills to the test!

1. What is a variable in JavaScript? 

a) A keyword used to perform arithmetic operations.

b) A container for storing data values.

c) A built-in function for displaying output on the screen.

d) A data type representing text and characters.

Answer:

b) A container for storing data values.

Explanation:

In JavaScript, a variable is a container used to store data values, such as numbers, strings, objects, or any other type of data.

2. What is the correct way to declare a variable in JavaScript?

a) variable x = 10;

b) var x = 10;

c) x = 10;

d) int x = 10;

Answer:

b) var x = 10;

Explanation:

In JavaScript, variables are declared using the 'var' keyword, followed by the variable name and an optional initial value.

3. What is the result of the following code?

var x = 5;
var y = 10;
var result = x + y;

a) 15

b) "15"

c) "510"

d) Syntax Error

Answer:

a) 15

Explanation:

The code declares two variables x and y with the values 5 and 10, respectively. Then, it assigns the sum of x and y to the variable result. The sum of 5 and 10 is 15.

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

a) myVariable

b) _value

c) 1count

d) $price

Answer:

c) 1count

Explanation:

Variable names in JavaScript cannot start with a number. Therefore, 1count is not a valid variable name.

Variables Naming Conventions:

Use Camel Case

Begin with Letters, $, or _

Avoid Reserved Words

Be Descriptive

Don't Use Hyphens (-)

Case Sensitive

Avoid Global Variables

5. Which keyword is used to declare block-scoped variables in ES6?

a) var

b) let

c) const

d) variable

Answer:

b) let

Explanation:

In ES6, the let keyword is used to declare block-scoped variables that are limited to the block (enclosing curly braces) in which they are defined.

6. What is the difference between let and const in JavaScript?

a) let is used for constant values, while const is used for variables.

b) let can be reassigned, while const is read-only and cannot be reassigned.

c) let is block-scoped, while const is function-scoped.

d) There is no difference; let and const are interchangeable.

Answer:

b) let can be reassigned, while const is read-only and cannot be reassigned.

Explanation:

In JavaScript ES6, let allows variables to be reassigned with new values, while const declares read-only variables that cannot be reassigned once they are initialized.

7. What is the purpose of the const keyword in JavaScript?

a) To declare a constant value that cannot be changed after initialization.

b) To declare a variable with block scope.

c) To define a function in JavaScript.

d) To store multiple values in an array.

Answer:

a) To declare a constant value that cannot be changed after initialization.

Explanation:

The const keyword is used to declare a constant variable in JavaScript. Once a value is assigned to a const variable, it cannot be reassigned or changed throughout the program's execution.

8. What is the difference between declaring a variable with var and let?

a) var is block-scoped, while let is function-scoped.

b) var variables can be reassigned, while let variables cannot.

c) var variables are limited to the block in which they are defined, while let variables are accessible throughout the entire function.

d) There is no difference; var and let can be used interchangeably.

Answer:

c) var variables are limited to the block in which they are defined, while let variables are accessible throughout the entire function.

Explanation:

The difference lies in their scope. var variables are function-scoped, whereas let variables are block-scoped. var variables are accessible throughout the entire function in which they are defined, while let variables are limited to the block in which they are defined.

9. What will be the value of the variable result in the following code?

let value = 20;
if (value > 10) {
  var result = "Greater than 10";
  console.log(result);
} else {
  var result = "Less than or equal to 10";
  console.log(result);
}

a) "Greater than 10"

b) "Less than or equal to 10"

c) "20"

d) Syntax Error

Answer:

a) "Greater than 10"

Explanation:

In this code, the if condition (value > 10) is true because value is 20, which is greater than 10. Therefore, the first var result declaration will be executed, resulting in the value "Greater than 10".

10. JavaScript variables are:

a. Case-insensitive

b. Case-sensitive

c. Neither case-insensitive nor case-sensitive

d. Case-sensitive only in strict mode

Answer:

b. Case-sensitive

Explanation:

JavaScript variable names are case-sensitive, meaning that myVariable and myvariable are different variables.

Conclusion

Congratulations on completing the JavaScript Variables quiz! Understanding variables is fundamental to programming in JavaScript. By mastering variables and their scope, you can effectively store and manipulate data in your applications. Keep practicing and exploring more JavaScript concepts to become a skilled developer. Happy coding!