What is a Memory Leak?

A memory leak occurs when a program allocates memory but fails to release it back to the system, even when the memory is no longer needed. Over time, these accumulated unreleased memory blocks can cause your application to consume more and more memory, potentially leading to:

• Degraded application performance
• System slowdowns
• Application crashes (Out of Memory errors)
• Server instability in production environments

How Memory Management Works

To understand memory leaks, it's essential to understand how memory management works in different environments:

Garbage-Collected Languages

Languages like JavaScript, Java, Kotlin, Go and Python use automatic memory management through garbage collection:

1. Allocation: Objects are created and memory is allocated
2. Usage: Application uses the allocated objects
3. Garbage Collection: Runtime automatically frees memory for objects that are no longer reachable

// Memory is allocated when creating the object
let user = { name: "John", age: 30 };

// Memory is automatically freed when 'user' goes out of scope
// and no other references exist

Manual Memory Management

Languages like C and C++ require explicit memory management:

// Manual allocation
char* buffer = malloc(1024);

// Must manually free the memory
free(buffer);

Types of Memory Leaks

1. Classical Memory Leaks

Memory that is allocated but never freed, even when no longer accessible.

2. Logical Memory Leaks

Memory that is still referenced by the application but no longer serves any useful purpose.

3. Temporary Memory Leaks

Memory that is eventually freed but held for much longer than necessary.

Common Causes in Different Languages

JavaScript/TypeScript

• Global variables that accumulate data
• Event listeners not properly removed
• Closures holding references to large objects
• Detached DOM nodes

Java/Kotlin

• Collections that grow without bounds
• Listeners and callbacks not unregistered
• ThreadLocal variables not cleaned up
• ClassLoader leaks

Go

• Goroutines that never terminate
• Channels that are never closed
• Global variables accumulating data
• Circular references in data structures

Memory Leak Example

Here's a simple example of a memory leak in JavaScript:

// BAD: This creates a memory leak
let users = [];

function addUser(name) {
    users.push({
        name: name,
        timestamp: new Date(),
        data: new Array(1000000).fill('x') // Large object
    });
    // users array keeps growing and never shrinks!
}

setInterval(() => {
    addUser(`User-${Date.now()}`);
}, 1000);

// GOOD: This prevents the memory leak
let users = [];
const MAX_USERS = 100;

function addUser(name) {
    users.push({
        name: name,
        timestamp: new Date(),
        data: new Array(1000000).fill('x')
    });

    // Keep only the last MAX_USERS entries
    if (users.length > MAX_USERS) {
        users.splice(0, users.length - MAX_USERS);
    }
}

Signs of Memory Leaks

Performance Indicators

• Gradual performance degradation over time
• Increasing memory usage without corresponding workload increase
• Frequent garbage collection pauses
• Out of Memory errors in production

Monitoring Metrics

• Heap size continuously growing
• Memory usage not returning to baseline after operations
• GC pressure increasing over time

Impact on Applications

Development Environment

• Slower development and testing cycles
• Increased resource requirements for development machines

Production Environment

• Scalability issues: Servers requiring more memory than expected
• Reliability problems: Applications crashing unexpectedly
• Cost implications: Higher infrastructure costs
• User experience: Slower response times and timeouts

Prevention Overview

While we'll cover detailed prevention strategies in later sections, the key principles are:

1. Understand object lifecycles in your application
2. Clean up resources explicitly when possible
3. Use profiling tools to monitor memory usage
4. Implement monitoring in production environments
5. Follow language-specific best practices

Next Steps

Now that you understand what memory leaks are, let's explore:

• Why Memory Leaks Matter - The real-world impact

Or jump directly to your language of interest:

• JavaScript/TypeScript