Memory Management

TL;DR

Memory in Node.js is managed by the V8 JavaScript engine. It is divided into two primary regions: the Stack (for static data and function execution context) and the Heap (for dynamic objects and arrays). V8 automatically allocates and frees memory using Garbage Collection.

Mental Model

How It Works

1. Stack: A LIFO (Last-In-First-Out) data structure that stores primitive types (Number, String, Boolean) and object references (pointers). It is very fast and managed automatically as functions are called and return.
2. Heap: A large unstructured region of memory where reference types (Objects, Arrays, Functions) are stored.
3. Resident Set Size (RSS): The total memory allocated for the Node process execution, which includes the V8 Heap, the V8 Stack, and C++ bindings/buffers.

Example

function allocateMemory() {
    // 'id' is a primitive. It is stored on the Stack.
    const id = 123; 

    // 'user' is an object. The object itself is stored in the Heap.
    // The variable 'user' (the pointer/reference) is stored on the Stack.
    const user = { name: "Alice", age: 30 }; 
}

allocateMemory();
// After the function returns, the Stack memory (id, user pointer) is cleared immediately.
// The object { name: "Alice", ... } remains in the Heap until Garbage Collected.

Common Interview Questions

What is the default memory limit in Node.js?

By default, the V8 heap limit is roughly 1.4 GB on 64-bit systems (and 700 MB on 32-bit). If your application exceeds this, it will crash with an Out of Memory (OOM) error.

How can you increase the Node.js memory limit?

You can increase the limit by passing the --max-old-space-size flag when starting Node.js.
node --max-old-space-size=4096 index.js (Sets the limit to 4GB).