structuredClone

JavaScriptJunior~2 min read

structuredClone() is a built-in JavaScript function that makes a deep copy of any value, including complex objects, arrays, maps, and even dates.

This is the most modern and safest way to clone data in JS without third-party libraries.

In short

javascript

const clone = structuredClone(value);

It creates a fully independent copy of the object, including all nested structures, and returns a new object with no shared references to the original.

Example

javascript

const user = {
  name: 'Tim',
  address: { city: 'Berlin' },
  hobbies: ['sport', 'music']
};

const clone = structuredClone(user);

clone.address.city = 'Lviv';
clone.hobbies.push('coding');

console.log(user.address.city); // "Berlin"
console.log(user.hobbies);      // ['sport', 'music']

The copy is deep - all nested objects and arrays are recreated. The original stays unchanged.

What `structuredClone` can copy

Supports:

objects ({}), arrays ([])
nested structures of any depth
Date
Map, Set
Blob, File, ArrayBuffer, TypedArray
RegExp (preserves the pattern and flags)
even circular references (unlike JSON.stringify())

Example with Map and Date

javascript

const data = {
  date: new Date(),
  map: new Map([['a', 1], ['b', 2]])
};

const copy = structuredClone(data);

console.log(copy.date === data.date); // false (a new object)
console.log(copy.map.get('a'));       // 1

Example with a circular reference (it works!)

javascript

const obj = {};
obj.self = obj;

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

structuredClone() handles even self-references, where JSON.parse(JSON.stringify()) would simply fail with an error.

What is not copied

Does not support:

functions
DOM elements
classes / prototypes
Symbol
undefined as a key

javascript

const obj = {
  fn: () => {},
  el: document.body
};

structuredClone(obj);
// Error: function or DOM node cannot be cloned

Comparison with other methods

Method	Copy type	Copies nested data	Copies functions	Copies Date / Map / Set
`{ ...obj }`	shallow	No	Yes	No
`Object.assign()`	shallow	No	Yes	No
`JSON.parse(JSON.stringify())`	deep	Yes	No	No
`structuredClone()`	deep	Yes	No	Yes
`_.cloneDeep()` (Lodash)	deep	Yes	No	Yes

Support

Works:

in all modern browsers (Chrome 98+, Firefox 94+, Edge 98+, Safari 15.4+)
in Node.js 17+
in Deno

For older environments you can add a polyfill, for example:

javascript

npm install core-js

SUMMARY

Property	`structuredClone()`
Copy type	Deep
Changes the original	No
Copies objects, arrays, Map, Set, Date	Yes
Works with circular references	Yes
Copies functions / DOM elements	No
Safe and built-in	Yes

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