Lodash _.clone vs Shallow Clone in JavaScript

This article explains the relationship and technical distinctions between a general shallow clone in native JavaScript and the _.clone utility provided by the Lodash library. While Lodash's _.clone is fundamentally an implementation of a shallow copy, it differs significantly from native shallow cloning techniques—such as object spread syntax and Object.assign—in how it handles specialized data structures, prototypes, and edge cases.

The Definition of a Shallow Clone

In JavaScript, a shallow clone creates a new compound object and copies the top-level properties from the original source. If a property is a primitive value (like a string, number, or boolean), the value itself is copied. However, if a property is a reference type (like an array or nested object), only the memory reference is copied. As a result, mutations made to nested objects in the clone directly affect the original object.

Native JavaScript provides two common ways to perform a shallow clone:

• The spread operator: { ...original } or [ ...original ]
• Object.assign(): Object.assign({}, original)

What Lodash _.clone Does

The _.clone function in Lodash is explicitly a shallow clone algorithm, distinct from _.cloneDeep, which recursively traverses and duplicates nested trees.

Like native techniques, _.clone does not duplicate nested objects; references to nested structures are shared between the clone and the source. However, _.clone is an advanced shallow clone implementation engineered to support diverse JavaScript types that standard native methods fail to duplicate properly.

Key Differences

1. Handling of Specialized Objects

Native shallow copying techniques are designed for plain objects and arrays. When applied to complex native types, native cloning mechanisms produce broken or empty objects:

• Date Objects: Spreading a Date instance ({ ...new Date() }) returns an empty object {} because Date properties are not enumerable. In contrast, _.clone(new Date()) produces a valid, functioning Date instance with the same timestamp.
• RegExp Objects: { .../abc/g } produces an empty object. _.clone(/abc/g) produces a new, properly configured RegExp instance.
• Maps and Sets: Native object spread on a Map or Set loses all stored entries. Lodash _.clone produces a new Map or Set containing the shallow elements of the original collection.
• ArrayBuffers and TypedArrays: Native methods cannot duplicate buffer allocations. Lodash _.clone properly allocates a new buffer and duplicates the binary data.

2. Prototype Preservation

Native shallow copy methods, such as Object.assign() or { ...obj }, always return instances inheriting from Object.prototype, stripping any custom prototype chains:

class User {
  greet() { return "Hello"; }
}

const user = new User();
const spreadClone = { ...user };
const lodashClone = _.clone(user);

console.log(spreadClone instanceof User); // false (prototype lost)
console.log(lodashClone instanceof User); // true (prototype preserved)

_.clone checks the prototype of custom instances and constructs the new shallow copy using the original prototype, preserving class methods and inheritance chains.

3. Primitive Safety and Robustness

Native mechanisms can produce runtime exceptions or unexpected structures when non-object types are provided. Lodash's _.clone contains built-in type checks: passing a primitive (e.g., a number or string), null, or undefined returns the value safely without throwing an error.

Summary

_.clone is not fundamentally different in concept from a shallow clone; rather, it is a robust, type-aware implementation of one. While native methods like { ...obj } and Object.assign are optimized for plain objects, Lodash's _.clone handles custom classes, Date, RegExp, Map, Set, and binary buffers, making it a more dependable choice when copying values of arbitrary or specialized types.