JavaScript Memory Management - Practice Questions 2026
Course Description
Mastering memory management is the hallmark of a senior JavaScript developer. While many programmers rely on the garbage collector to handle the heavy lifting, understanding the underlying mechanics is essential for building high-performance, leak-free applications. This course provides a rigorous, comprehensive suite of practice exams designed to bridge the gap between theoretical knowledge and professional expertise.
Why Serious Learners Choose These Practice Exams
Serious learners understand that watching a video is not the same as mastering a concept. These practice exams are crafted to challenge your intuition and force you to think like the V8 engine. By engaging with these questions, you will move beyond syntax and begin to understand how your code interacts with the physical hardware. We focus on the "why" behind memory allocation, the "how" of garbage collection algorithms, and the "what" of performance optimization.
Course Structure
This curriculum is meticulously organized to take you from foundational understanding to architectural mastery.
Basics / Foundations
This section covers the entry-level concepts of the memory lifecycle: allocation, usage, and release. You will explore the differences between the Stack and the Heap, understanding which types of data go where and why primitive types are handled differently than objects.
Core Concepts
Dive deeper into how JavaScript handles references. We explore the "Reachability" concept, the Root (global object), and how the Garbage Collector determines what can be safely purged from memory.
Intermediate Concepts
Focus on the "Mark-and-Sweep" algorithm and the generational collection strategy (New Space vs. Old Space). This section challenges your knowledge of Scavenging and how long-lived objects are promoted within the heap.
Advanced Concepts
Explore complex topics like Closures, the hidden memory costs of Lexical Environments, and the behavior of WeakMap and WeakSet. You will learn how to identify specific patterns that lead to memory bloat in large-scale applications.
Real-world Scenarios
Practicality is key. This section simulates real-world debugging. You will analyze code snippets involving Event Listeners, Timers, and DOM references to identify where "Detached DOM nodes" occur and how to fix them.
Mixed Revision / Final Test
A comprehensive final evaluation that mixes all difficulty levels. This simulates a high-pressure technical interview or a certification environment, ensuring you are ready for any professional challenge.
Sample Practice Questions
Question 1
Consider the following code: Let a = { name: "John" }; let b = a; a = null; What happens to the object originally referenced by 'a' in memory?
Option 1: The object is immediately collected by the Garbage Collector.
Option 2: The object remains in memory because 'b' still holds a reference to it.
Option 3: The object is moved to the "Old Space" of the heap.
Option 4: A ReferenceError is thrown because 'a' is null.
Option 5: The object becomes a "Detached" node.
Correct Answer: Option 2
Correct Answer Explanation
In JavaScript, the Garbage Collector uses reachability. Even though the reference 'a' was set to null, the object { name: "John" } is still reachable through the variable 'b'. As long as there is at least one path from the root to the object, it will not be collected.
Wrong Answers Explanation
Option 1: Incorrect because the Garbage Collector only removes unreachable objects. 'b' makes it reachable.
Option 3: Incorrect because "Old Space" promotion is based on the object's survival through multiple GC cycles, not the nullification of a single reference.
Option 4: Incorrect. Setting a variable to null is a valid assignment and does not trigger an error.
Option 5: Incorrect. "Detached" nodes specifically refer to DOM elements that are no longer in the document tree but are still referenced by JavaScript.
Question 2
Which of the following is a primary reason why a WeakMap is used instead of a standard Map for memory management?
Option 1: WeakMaps allow for faster iteration over keys.
Option 2: WeakMaps allow for primitive types to be used as keys.
Option 3: WeakMaps do not prevent garbage collection of their key objects.
Option 4: WeakMaps automatically clear their values when the heap is 90% full.
Option 5: WeakMaps use the Stack instead of the Heap for storage.
Correct Answer: Option 3
Correct Answer Explanation
WeakMaps hold "weak" references to their keys. If there are no other strong references to an object used as a key in a WeakMap, the Garbage Collector can reclaim that object and subsequently remove the corresponding entry from the WeakMap. This prevents memory leaks in scenarios like caching or metadata storage.
Wrong Answers Explanation
Option 1: Incorrect. WeakMaps are actually not iterable; you cannot loop through them.
Option 2: Incorrect. WeakMap keys must be objects (or certain types of symbols), not primitives.
Option 3: Incorrect. This is a made-up behavior; GC is not triggered by a specific percentage threshold of a single Map.
Option 5: Incorrect. All objects, including WeakMaps and their entries, are stored in the Heap.
Welcome to the best practice exams to help you prepare for your JavaScript Memory Management studies.
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