deepClone()

deepClone<T>(value): T

Creates a deep clone of a value, recursively cloning nested structures.

Handles primitives, arrays, Date, Map, Set, RegExp, Error, and plain objects. Preserves prototypes and symbol keys. Handles circular references. Functions are copied by reference (not cloned).

For TypedArrays, ArrayBuffer, Buffer, Blob, File, use deepCloneFull instead.

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Type Parameters

T: T

The type of the destination object.

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Parameters

value: T

The value to deep clone.

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Returns: T

A deep clone of the value.

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Since

2.0.0

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Performance

O(n) time & space where n is total number of properties/elements.

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Also known as

clone (Remeda, Ramda) · cloneDeep (Lodash, es-toolkit, Radashi) · ❌ (Effect, Modern Dash, Antfu)

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Examples

const original = { a: 1, b: { c: 2 }, d: [3, 4] };
const cloned = deepClone(original);
cloned.b.c = 99;
original.b.c; // => 2 (unchanged)

const circular: `Record<string, unknown>` = { a: 1 };
circular.self = circular;
const cloned = deepClone(circular);
cloned.self === cloned; // => true

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How it works?

Creates a deep copy of a value, recursively cloning all nested structures.

Independence

Circular Reference Handling

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Use Cases

Duplicate simple state 📌

Create a deep copy of an object to avoid mutation bugs. Essential for Redux-style state updates or immutable patterns.

#duplicate#clone#state#immutable#mutation#Redux

const newState = deepClone(currentState);
newState.user.isActive = true; // Safe mutation

Snapshot state history

Store copies of state at specific points in time for undo/redo functionality.

#snapshot#history#undo#redo#state#time-travel

const history = [];
function pushState(state) {
  history.push(deepClone(state));
}

Break references

Ensure that nested objects are fully decoupled from the original. Useful when passing data to components that might mutate it.

#break#references#decoupling#isolation#mutation#safety

const original = { config: { retries: 3 } };
const copy = deepClone(original);
copy.config.retries = 5;
console.log(original.config.retries); // 3

Clone form state for reset and dirty-checking

Store the initial form state to enable "Reset" and detect unsaved changes. Universal pattern for form-heavy applications with save/discard workflows.

#form#reset#dirty#checking#clone#original#comparison#state

const initialValues = deepClone(formData);

// User edits the form...
formData.name = "Updated Name";
formData.address.city = "New City";

// Dirty check: compare current state with original
const hasChanges = JSON.stringify(formData) !== JSON.stringify(initialValues);
// => true

// Reset: restore original values
function resetForm() {
  Object.assign(formData, deepClone(initialValues));
}