Understanding JavaScript Memory Management by Omiye PreciousUnderstanding JavaScript Memory Management by Omiye Precious

Understanding JavaScript Memory Management

Omiye Precious

Completed work

Technical Writer

Medium

Computer Software

Understanding JavaScript Memory Management

Omiye Precious

4 min read

Feb 17, 2025

Memory management is an important aspect of JavaScript programming as far as performance and reliability of applications are concerned. Unlike lower level languages like C and C++, JavaScript automatically manages memory using a process called garbage collection.

However, poor memory usage causes performance issues like memory leaks, underperforming speeds, and higher resource consumption. This article discusses the memory management model of JavaScript within which common memory problems exist and ways to ensure usage of memory is optimized.

JavaScript Memory Lifecycle

JavaScript has a three-stage memory lifecycle:

Memory Allocation: The engine allocates memory for any variable, object, or function once it is created.

Memory Usage: This is when a program runs and all the memory assigned to it is used for calculations along with some object manipulations.

Memory Deallocation: Garbage collector automatically deallocates objects that are no longer used and releases the memory again.

Memory Allocation in JavaScript

Let’s explore the JavaScript memory allocation:

Primitive and Reference Types

Primitive Data Types: Stored directly in stack memory such as string, number, Boolean, null, undefined, symbol, bigint.

Reference Data Types: Stored under heap memory with a reference in the stack like objects, arrays, and functions.

Stack and Heap Memory Allocation

Stack Memory: It stores function calls and primitive values.

Heap Memory: It stores objects and complex structures.

Example of Memory Allocation

let a = 10; // Stored in stacklet obj = { name: "John" }; // Object stored in heap, reference stored in stack

Understanding JavaScript Garbage Collection(GC)

GC is an automated process for freeing memory, which becomes available by releasing objects that are no longer in use. In practice, however, the most well-known algorithms in JavaScript are the mark-and-sweep and Reference counting and Cyclic method.

Mark-and-Sweep Algorithm

Marking Phase: In this phase, the garbage collector walks through the object graph, marking all objects that are still reachable.

Sweeping Phase: The unreachable objects are removed from the memory.

Reference Counting and Cyclic References

Reference counting keeps track of all references to an object. When the count reaches zero, the object is collected.

Cyclic references (e.g., two objects referencing each other) may possibly cause memory leaks.

Example of a cyclic reference:

let obj1 = {};let obj2 = {};obj1.ref = obj2;obj2.ref = obj1; // Neither object is eligible for garbage collection

Common Memory Issues and Leaks

Below are some of the common memory issues and leaks:

Unintended Global Variables

The function below creates an implicit global variable name, causing potential issues.

function myFunc() {    name = "John"; // Implicit global variable (memory leak)}

Closures Holding References

The function below creates a closure that prevents bigData from being garbage collected.

function outer() {    let bigData = new Array(1000000); // Large array    return function inner() {        console.log(bigData.length);    };}let closure = outer(); // `bigData` is not garbage collected

Detached DOM Elements

The code below select a button with the ID `myButton`, and adds a click event listener that logs `Clicked`, then it removes the button from the DOM.

let button = document.getElementById("myButton");button.addEventListener("click", function() {    console.log("Clicked");});button.remove(); // Event listener may still hold reference to the button

Caching Issues and Memory Bloat

One critical issue elicited by storing a large object is persistent storage in cache. This can occasionally create the memory leak problem by prolonging the useful life of an object, therefore postponing its garbage collection and subsequent disposal of its memory.

Best Practices for Efficient Memory Management

Avoid Unintentional Global Variables: Just always declare variables using let, const, or var.

Use WeakMap and WeakSet for Short-lived References: In general, they will not preserve the keys from garbage collection.

let wm = new WeakMap();let obj = {};wm.set(obj, "value");obj = null; // Object is garbage collected

Optimize DOM Manipulations: Remove all the event listeners from domination or unused elements.

function cleanup() {    document.getElementById("myButton").removeEventListener("click", handler);}

Manage Event Listeners and Subscriptions: Unsubscribe from the event listeners and observables when not required anymore.

Use Efficient Data Structures: Prefer using arrays over objects where possible for improved memory health management.

Tools for Monitoring and Debugging Memory Usage

Chrome DevTools Memory Panel

Take heap snapshots to analyze how memory is being used.

It is used to identify memory leaks and detached DOM elements.

Heap Snapshots and Memory Profiling

In order to manage performance, use the Performance tab to detect memory issues and high consumption of memory.

Example: Open DevTools → Performance → Start profiling.

Performance Audits with Lighthouse

Ensure Lighthouse contains audits meant to highlight performance recommendations invoked by memory concerns.

Conclusion

Effective memory management in JavaScript is concerned about the performance of the application as well as avoiding the unwanted space in the memory. Knowing how memory is used, how garbage collection works, and the not-so-obvious pitfalls will help the developer in writing optimized and efficient codes. Following best practices and using debugging tools ensures that applications will run with minimum response time. Continuous monitoring and optimization remain essential for scalable web applications.

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Completed work

Posted Apr 14, 2025

Published an article on JavaScript memory management and optimization techniques.

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Timeline

Feb 14, 2025 - Feb 17, 2025

Understanding JavaScript Memory Management

Omiye Precious

Completed work

Technical Writer

Medium

Computer Software

Understanding JavaScript Memory Management

Omiye Precious

4 min read

Feb 17, 2025

JavaScript Memory Lifecycle

JavaScript has a three-stage memory lifecycle:

Memory Allocation: The engine allocates memory for any variable, object, or function once it is created.

Memory Usage: This is when a program runs and all the memory assigned to it is used for calculations along with some object manipulations.

Memory Deallocation: Garbage collector automatically deallocates objects that are no longer used and releases the memory again.

Memory Allocation in JavaScript

Let’s explore the JavaScript memory allocation:

Primitive and Reference Types

Primitive Data Types: Stored directly in stack memory such as string, number, Boolean, null, undefined, symbol, bigint.

Reference Data Types: Stored under heap memory with a reference in the stack like objects, arrays, and functions.

Stack and Heap Memory Allocation

Stack Memory: It stores function calls and primitive values.

Heap Memory: It stores objects and complex structures.

Example of Memory Allocation

let a = 10; // Stored in stacklet obj = { name: "John" }; // Object stored in heap, reference stored in stack

Understanding JavaScript Garbage Collection(GC)

Mark-and-Sweep Algorithm

Marking Phase: In this phase, the garbage collector walks through the object graph, marking all objects that are still reachable.

Sweeping Phase: The unreachable objects are removed from the memory.

Reference Counting and Cyclic References

Reference counting keeps track of all references to an object. When the count reaches zero, the object is collected.

Cyclic references (e.g., two objects referencing each other) may possibly cause memory leaks.

Example of a cyclic reference:

let obj1 = {};let obj2 = {};obj1.ref = obj2;obj2.ref = obj1; // Neither object is eligible for garbage collection

Common Memory Issues and Leaks

Below are some of the common memory issues and leaks:

Unintended Global Variables

The function below creates an implicit global variable name, causing potential issues.

function myFunc() {    name = "John"; // Implicit global variable (memory leak)}

Closures Holding References

The function below creates a closure that prevents bigData from being garbage collected.

function outer() {    let bigData = new Array(1000000); // Large array    return function inner() {        console.log(bigData.length);    };}let closure = outer(); // `bigData` is not garbage collected

Detached DOM Elements

The code below select a button with the ID `myButton`, and adds a click event listener that logs `Clicked`, then it removes the button from the DOM.

let button = document.getElementById("myButton");button.addEventListener("click", function() {    console.log("Clicked");});button.remove(); // Event listener may still hold reference to the button

Caching Issues and Memory Bloat

Best Practices for Efficient Memory Management

Avoid Unintentional Global Variables: Just always declare variables using let, const, or var.

Use WeakMap and WeakSet for Short-lived References: In general, they will not preserve the keys from garbage collection.

let wm = new WeakMap();let obj = {};wm.set(obj, "value");obj = null; // Object is garbage collected

Optimize DOM Manipulations: Remove all the event listeners from domination or unused elements.

function cleanup() {    document.getElementById("myButton").removeEventListener("click", handler);}

Manage Event Listeners and Subscriptions: Unsubscribe from the event listeners and observables when not required anymore.

Use Efficient Data Structures: Prefer using arrays over objects where possible for improved memory health management.

Tools for Monitoring and Debugging Memory Usage

Chrome DevTools Memory Panel

Take heap snapshots to analyze how memory is being used.

It is used to identify memory leaks and detached DOM elements.

Heap Snapshots and Memory Profiling

In order to manage performance, use the Performance tab to detect memory issues and high consumption of memory.

Example: Open DevTools → Performance → Start profiling.

Performance Audits with Lighthouse

Ensure Lighthouse contains audits meant to highlight performance recommendations invoked by memory concerns.

Conclusion

Like this project

Completed work

Posted Apr 14, 2025

Published an article on JavaScript memory management and optimization techniques.

Likes

Views

Timeline

Feb 14, 2025 - Feb 17, 2025