Mastering Deep Object Cloning in JavaScript with structuredClone()

Deep cloning in JavaScript has always been tricky. Developers often relied on hacks like JSON.stringify() + JSON.parse() or external libraries, which only worked for the simplest cases. But now, there’s a native and powerful alternative: structuredClone().

In this guide, you’ll learn how structuredClone() works, what it supports, where it breaks, how it compares to other methods, and where to use it in real-world apps.

🔄 Why structuredClone() Is Not Just JSON 2.0

Let’s start with a classic problem.

const data = {
  date: new Date(),
  regex: /hello/gi,
  map: new Map([['key', 'value']]),
};

const jsonCopy = JSON.parse(JSON.stringify(data));
console.log(jsonCopy);
// Output: { date: "2025-02-02T12:00:00.000Z", regex: {}, map: {} }

You lose critical types:

• Date becomes a string
• RegExp becomes an empty object
• Map becomes

Worse, if your object has circular references, it’ll crash:

const node = {};
node.self = node;

JSON.stringify(node); // ❌ TypeError: Converting circular structure to JSON

Enter structuredClone():

const structuredCopy = structuredClone(data);

console.log(structuredCopy.date instanceof Date); // true
console.log(structuredCopy.regex instanceof RegExp); // true
console.log(structuredCopy.map instanceof Map); // true

It handles these cases correctly, deeply, and safely.

✅ What structuredClone() Supports

This method works with a wide range of types:

✅ Primitives:

undefined, null, boolean, number, bigint, string, symbol

✅ Data Structures:

• Objects and arrays
• Date, RegExp, Map, Set
• Typed arrays, ArrayBuffer, SharedArrayBuffer
• Blob, File, ImageData, MessagePort, FileList
• Browser-specific objects like MessageChannel, OffscreenCanvas

🔬 Binary Example:

const buffer = new ArrayBuffer(16);
const clone = structuredClone(buffer);

console.log(clone.byteLength); // 16
console.log(clone === buffer); // false

Useful for transferring binary data to Web Workers or BroadcastChannel.

🔁 Deep Nesting and Circular Structures

structuredClone() can also handle circular references:

const node = { value: 1 };
node.self = node;

const clone = structuredClone(node);
console.log(clone.self === clone); // true

This makes it perfect for serializing graphs, trees, and cyclic structures, where JSON completely fails.

🧱 Limitations of structuredClone()

While powerful, it doesn’t handle everything.

❌ 1. Functions

const withFn = {
  sayHi: () => console.log('hi'),
};

structuredClone(withFn); // ❌ DataCloneError

Functions can’t be cloned. Behavior (code) is lost.

❌ 2. DOM Elements

const div = document.createElement('div');
structuredClone(div); // ❌ DataCloneError

UI elements aren’t cloneable — only data is.

❌ 3. Prototypes and Class Instances

class MyClass {
  constructor(x) {
    this.x = x;
  }
}

const instance = new MyClass(42);
const clone = structuredClone(instance);

console.log(clone instanceof MyClass); // false
console.log(clone.x); // 42

Only the plain object structure is cloned — not the prototype chain.

⚖️ Performance: Is It Slow?

Compared to JSON.parse(JSON.stringify(...)), yes — structuredClone() is slower for flat structures.

But it’s much more stable, and actually faster for:

• Nested or deeply recursive objects
• Objects with circular references
• Binary data or typed arrays

If performance is critical (e.g., cloning every animation frame), consider alternatives like Object.assign() (shallow) or lodash/cloneDeep.

🆚 Alternatives and Polyfills

📦 Lodash cloneDeep

import cloneDeep from 'lodash/cloneDeep';

import cloneDeep from 'lodash/cloneDeep';

const obj = { a: 1, b: { c: 2 } };
const deep = cloneDeep(obj);

Works for nested objects and arrays — but:

• Can’t clone Map, Set, Date accurately
• Won’t handle circular structures unless configured

🌐 Browser Support

• ✅ Supported: Chrome 98+, Firefox 94+, Safari 15+, Node.js 17+
• ❌ Not Supported: IE11, Safari < 14, Node < 17

For older environments, use:

• structured-clone polyfill
• Fallback to cloneDeep() or JSON.parse() with checks

🚀 Real-World Use Cases

1. Undo/Redo in Rich Editors

When building complex editors (think Notion, Figma, Miro), you need to clone the entire state, including nested structures, maps, and cyclic references.

function saveSnapshot(state) {
  historyStack.push(structuredClone(state));
}

• Preserves deep state
• Avoids accidental mutations
• Eliminates bug-prone manual deep clones

2. State Sync Between Tabs with BroadcastChannel

const channel = new BroadcastChannel('sync');
channel.postMessage(structuredClone(store));

On receiving:

channel.onmessage = e => {
  syncWithStore(e.data);
};

Ensures:

• Map, Date, Blob stay intact
• Cycles don’t crash the sync
• Fast, native serialization

3. Passing Data to Web Workers

const worker = new Worker('worker.js');
worker.postMessage(structuredClone(bigData));

Structured clone avoids Transferable limitations and keeps data safe.

⚠️ When Not to Use It

🧠 Final Thoughts

structuredClone() is the modern way to deep clone in JavaScript:

• Safe
• Native
• Handles complex structures and cycles
• Ideal for serialization, syncing, undo stacks

It’s especially powerful in React, Vue, and Svelte apps for state snapshotting, and is perfect for passing data to IndexedDB, postMessage, or between browser tabs.

Use it with care — know where it shines and where it doesn’t. And say goodbye to JSON.parse(JSON.stringify(...)) once and for all.