JavaScript Variables & Data Types - Practice Questions 2026

Name: JavaScript Variables & Data Types - Practice Questions 2026
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Course Description

Master the fundamentals of web development with our comprehensive JavaScript Variables & Data Types Practice Exams. This course is specifically designed to bridge the gap between theoretical knowledge and practical coding proficiency. Whether you are preparing for a technical interview or looking to solidify your understanding of JavaScript's core mechanics, these practice tests provide the rigorous training you need.

Why Serious Learners Choose These Practice Exams

Serious learners understand that watching tutorials is only half the battle. To truly master JavaScript, you must test your ability to identify edge cases, understand memory allocation, and predict output accurately. Our practice exams stand out because they go beyond simple definitions. We focus on deep comprehension, ensuring you understand the "why" behind every variable declaration and data transformation. This course is built for those who want to eliminate guesswork and write predictable, bug-free code.

Course Structure

Our practice exams are organized into a logical progression to ensure you build confidence as you advance through the material:

Basics / Foundations: This section focuses on the fundamental syntax of JavaScript. You will be tested on variable declaration keywords such as var, let, and const. It covers naming conventions and the basic concept of assignment.

Core Concepts: Here, we dive into the primitive data types including Strings, Numbers, Booleans, Null, and Undefined. You will learn to distinguish between these types and understand how JavaScript handles basic data storage.

Intermediate Concepts: This module explores type coercion, both implicit and explicit. You will tackle questions regarding template literals, the Symbol type, and the nuances of BigInt, as well as how different types interact during operations.

Advanced Concepts: Challenge yourself with complex topics such as Pass-by-Value vs. Pass-by-Reference. This section covers the differences between primitive types and Reference types (Objects, Arrays), including how they are stored in the heap and stack.

Real-world Scenarios: These questions simulate actual coding problems you will encounter in professional environments. You will need to debug snippets and choose the most efficient data structures for specific tasks.

Mixed Revision / Final Test: A comprehensive final exam that pulls questions from all previous sections. This timed environment is designed to simulate the pressure of a real technical assessment.

Sample Questions

Question 1

What is the output of the following code?

console. log(typeof typeof 42);

Option 1: "number"

Option 2: "string"

Option 3: "object"

Option 4: "undefined"

Option 5: TypeError

Correct Answer: Option 2

Correct Answer Explanation: The typeof operator returns a string representing the type of the operand. In the expression typeof 42, the result is the string "number". Therefore, the expression becomes typeof "number". Since "number" is a string, the final result is "string".

Wrong Answers Explanation:

Option 1: This is wrong because the first typeof already converted the number into a string.

Option 3: This is wrong because neither a number nor the string "number" is an object in this context.

Option 4: This is wrong because the value 42 and its type description are both defined.

Option 5: This is wrong because typeof is a very safe operator and does not throw errors even for undeclared variables.

Question 2

Which of the following statements is true regarding const declarations in JavaScript?

Option 1: They can be reassigned but not redeclared.

Option 2: They are hoisted and initialized with "undefined".

Option 3: They must be initialized at the time of declaration.

Option 4: They have function scope only.

Option 5: They create a deep-frozen, immutable object.

Correct Answer: Option 3

Correct Answer Explanation: Unlike let or var, a const variable must be assigned a value during the declaration statement. Failure to do so will result in a SyntaxError.

Wrong Answers Explanation:

Option 1: This is wrong because const creates a constant reference; the value/reference cannot be reassigned.

Option 2: This is wrong because while const is hoisted, it is in the "Temporal Dead Zone" and is not initialized with "undefined".

Option 4: This is wrong because const is block-scoped, meaning it is restricted to the curly braces {} in which it is defined.

Option 5: This is wrong because while the reference is immutable, the properties of an object assigned to a const variable can still be modified.

Course Features

Welcome to the best practice exams to help you prepare for your JavaScript Variables & Data Types journey. By enrolling, you gain access to a premium learning environment: