JavaScript Basics - Practice Questions 2026

Mastering JavaScript requires more than just watching tutorials; it requires consistent practice and the ability to solve logical problems under pressure. This comprehensive practice exam course is designed to bridge the gap between theoretical knowledge and practical application. Whether you are preparing for a technical interview or looking to solidify your coding foundations, these exams provide the rigorous testing environment you need.

Why Serious Learners Choose These Practice Exams

Serious learners understand that passive learning leads to knowledge gaps. These exams are meticulously crafted to challenge your understanding of JavaScript mechanics. Unlike standard quizzes, our questions focus on "why" code behaves the way it does, ensuring you don't just memorize syntax but actually understand the engine behind the language.

Course Structure

This course is organized into six progressive modules, ensuring a smooth learning curve from syntax basics to complex architectural logic.

• Basics / Foundations: This section focuses on the essential building blocks of the language. You will be tested on variable declarations (var, let, const), data types, basic operators, and naming conventions.

• Core Concepts: Here, we dive deeper into control flow and structures. Expect questions on loops (for, while, do-while), conditional statements (if-else, switch), and the fundamental behavior of functions.

• Intermediate Concepts: This module covers the "heart" of JavaScript. We explore scope, hoisting, closures, and array methods like map, filter, and reduce. You will also encounter questions regarding object manipulation and prototypes.

• Advanced Concepts: Designed for those looking to reach seniority, this section tests your knowledge of Asynchronous JavaScript (Promises, async/await), the "this" keyword, the Event Loop, and advanced error handling.

• Real-world Scenarios: This module presents code snippets that mimic actual production bugs or feature requests. You must analyze the context to determine the most efficient or bug-free solution.

• Mixed Revision / Final Test: A comprehensive simulation of a real technical assessment. Questions are randomized across all difficulty levels to ensure you are fully prepared for any challenge.

Sample Practice Questions

Question 1

What is the output of the following code?

console . log(typeof NaN);

• Option 1: "NaN"

• Option 2: "undefined"

• Option 3: "number"

• Option 4: "object"

• Option 5: "null"

Correct Answer: Option 3

Correct Answer Explanation: In JavaScript, NaN stands for "Not-a-Number," but ironically, its technical data type is defined as a number according to the IEEE 754 floating-point standard. Therefore, typeof NaN returns "number".

Wrong Answers Explanation:

• Option 1: "NaN" is a value, not a string returned by the typeof operator.

• Option 2: undefined is returned for variables that have been declared but not assigned a value.

• Option 4: Objects are collections of properties; NaN is a primitive numeric value.

• Option 5: null represents the intentional absence of any object value and is its own distinct type (though typeof null famously returns "object" due to a legacy bug).

Question 2

Consider this code:

let a = [1, 2, 3]; let b = a; b . push(4); console . log(a);

What will be logged to the console?

• Option 1: [1, 2, 3]

• Option 2: [1, 2, 3, 4]

• Option 3: undefined

• Option 4: Error

• Option 5: [4]

Correct Answer: Option 2

Correct Answer Explanation: In JavaScript, arrays are reference types. When you assign a to b, both variables point to the same memory location. Modifying the array via variable b also affects variable a because they reference the same underlying object.

Wrong Answers Explanation:

• Option 1: This would only be true if arrays were value types (copied by value), which they are not.

• Option 3: The variable a is clearly defined and initialized, so it cannot be undefined.

• Option 4: The syntax is perfectly valid JavaScript; no error will be thrown.

• Option 5: The push method adds an element to the end of the existing array rather than replacing the entire array.

Welcome to the best practice exams to help you prepare for your JavaScript Basics

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We hope that by now you're convinced! And there are a lot more questions inside the course.