Lodash _.clone vs Shallow Copy Memory References

This article examines how memory referencing operates when using the Lodash _.clone method on an array of objects compared to standard shallow copy mechanisms in JavaScript. It outlines how reference allocation functions at both the array and element levels, demonstrates why nested object references remain linked, and contrasts these behaviors with deep cloning alternatives.

The Reality of Lodash _.clone

In the Lodash library, _.clone is an implementation of a shallow copy. Consequently, there is no fundamental memory referencing difference between Lodash's _.clone and native shallow copying operations, such as the spread operator ([...array]), Array.from(), or Array.prototype.slice().

Both approaches produce the exact same memory structure when applied to an array containing nested objects.

Outer Array Reference vs. Inner Object References

When you apply _.clone to an array of objects, the JavaScript engine allocates memory in two distinct ways:

  1. Outer Array (New Memory Address): A new array instance is allocated in heap memory with its own unique memory address. Because the outer reference is unique:

    • clonedArray === originalArray evaluates to false.
    • Modifying the array's structure—such as using push(), pop(), or reordering elements—affects only the cloned array and leaves the original array untouched.

  2. Inner Objects (Shared Memory Addresses): The elements within the array are not duplicated. Instead, the memory addresses (pointers) of the objects stored in the original array are copied directly into the new array. Because these references point to the same memory locations:

    • clonedArray[0] === originalArray[0] evaluates to true.
    • Mutating a property of an inner object (e.g., clonedArray[0].name = "Updated") directly alters the object in heap memory, instantly reflecting the change in originalArray[0].name.

Memory Behavior Demonstrated

const original = [{ id: 1, name: 'Alpha' }, { id: 2, name: 'Beta' }];

// Using Lodash _.clone
const lodashCloned = _.clone(original);

// Using native shallow copy
const nativeCloned = [...original];

// Array container references are independent
console.log(lodashCloned === original); // false
console.log(nativeCloned === original); // false

// Element references are identical across all instances
console.log(lodashCloned[0] === original[0]); // true
console.log(nativeCloned[0] === original[0]); // true

// Mutating a nested property mutates the shared heap object
lodashCloned[0].name = 'Omega';
console.log(original[0].name); // "Omega"

Breaking Object References with _.cloneDeep

To eliminate shared memory references entirely, a shallow copy is insufficient. Lodash provides the _.cloneDeep method for this purpose.

Unlike _.clone, _.cloneDeep recursively traverses the array and instantiates new memory allocations for every object and primitive found within. Under _.cloneDeep: