# @ungap/structured-clone

> A structuredClone polyfill

Latest version **1.4.0** (published 2026-08-27) · ISC license · 0 weekly downloads

## Install

```sh
npm install @ungap/structured-clone
pnpm add @ungap/structured-clone
yarn add @ungap/structured-clone
bun add @ungap/structured-clone
```

## Health

**Score 68/100 (B)** — status: active.

Positive: has types package; esm support; no vulnerabilities; recently updated; high maintenance score; high quality score.

Warnings: low downloads.

## Facts

| | |
|---|---|
| Version | 1.4.0 |
| Published | 2026-08-27 |
| First published | 2021-10-29 |
| Weekly downloads | 0 |
| License | ISC |
| TypeScript types | separate (@types/ungap__structured-clone) |
| Module format | ESM + CommonJS |
| Dependencies | 0 |
| Unpacked size | 29 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 324 |
| Author | Andrea Giammarchi |
| Maintainers | webreflection |
| Keywords | recursion, structured, clone, algorithm |

## Links

- npm: https://www.npmjs.com/package/@ungap/structured-clone
- Repository: https://github.com/ungap/structured-clone
- Homepage: https://github.com/ungap/structured-clone#readme
- Issues: https://github.com/ungap/structured-clone/issues
- npm.io page: https://npm.io/package/@ungap/structured-clone

## Recent versions

- 1.4.0 (latest) — 2026-08-27
- 1.3.4 — 2026-08-26
- 1.3.3 — 2026-07-10
- 1.3.2 — 2026-06-23
- 1.3.1 — 2026-05-06
- 1.3.0 — 2025-01-23
- 1.2.1 — 2024-12-07
- 1.2.0 — 2023-05-04
- 1.1.2 — 2023-05-03
- 1.1.1 — 2023-05-03
- 1.1.0 — 2023-04-29
- 1.0.2 — 2023-02-14
- 1.0.1 — 2022-05-11
- 1.0.0 — 2022-05-10
- 0.3.4 — 2021-11-07
- … 12 more at https://npm.io/package/@ungap/structured-clone/versions

## README

# structuredClone polyfill

[![Downloads](https://img.shields.io/npm/dm/@ungap/structured-clone.svg)](https://www.npmjs.com/package/@ungap/structured-clone) [![build status](https://github.com/ungap/structured-clone/actions/workflows/node.js.yml/badge.svg)](https://github.com/ungap/structured-clone/actions) [![Coverage Status](https://coveralls.io/repos/github/ungap/structured-clone/badge.svg?branch=main)](https://coveralls.io/github/ungap/structured-clone?branch=main)

An env agnostic serializer and deserializer with recursion ability and types beyond *JSON* from the *HTML* standard itself.

  * [Supported Types](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm#supported_types)
    * *not supported yet*: Blob, File, FileList, ImageBitmap, ImageData or others non *JS* types but typed arrays are supported without major issues, but u/int8, u/int16, and u/int32 are the only safely suppored (right now).
    * *not possible to implement*: the `{transfer: []}` option can be passed but it's completely ignored.
  * [MDN Documentation](https://developer.mozilla.org/en-US/docs/Web/API/structuredClone)
  * [Serializer](https://html.spec.whatwg.org/multipage/structured-data.html#structuredserializeinternal)
  * [Deserializer](https://html.spec.whatwg.org/multipage/structured-data.html#structureddeserialize)

Serialized values can be safely stringified as *JSON* too, and deserialization resurrect all values, even recursive, or more complex than what *JSON* allows.


### Examples

Check the [100% test coverage](./test/index.js) to know even more.

```js
// as default export
import structuredClone from '@ungap/structured-clone';
const cloned = structuredClone({any: 'serializable'});

// as independent serializer/deserializer
import {serialize, deserialize} from '@ungap/structured-clone';

// the result can be stringified as JSON without issues
// even if there is recursive data, bigint values,
// typed arrays, and so on
const serialized = serialize({any: 'serializable'});

// the result will be a replica of the original object
const deserialized = deserialize(serialized);
```

#### Global Polyfill
Note: Only monkey patch the global if needed. This polyfill works just fine as an explicit import: `import structuredClone from "@ungap/structured-clone"`
```js
// Attach the polyfill as a Global function
import structuredClone from "@ungap/structured-clone";
if (!("structuredClone" in globalThis)) {
  globalThis.structuredClone = structuredClone;
}

// Or don't monkey patch
import structuredClone from "@ungap/structured-clone"
// Just use it in the file
structuredClone()
```

**Note**: Do not attach this module's default export directly to the global scope, whithout a conditional guard to detect a native implementation. In environments where there is a native global implementation of `structuredClone()` already, assignment to the global object will result in an infinite loop when `globalThis.structuredClone()` is called. See the example above for a safe way to provide the polyfill globally in your project.

### Extra Features

There is no middle-ground between the structured clone algorithm and JSON:

  * JSON is more relaxed about incompatible values: it just ignores these
  * Structured clone is inflexible regarding incompatible values, yet it makes specialized instances impossible to reconstruct, plus it doesn't offer any helper, such as `toJSON()`, to make serialization possible, or better, with specific cases

This module specialized `serialize` export offers, within the optional extra argument, a **lossy** property to avoid throwing when incompatible types are found down the road (function, symbol, ...), so that it is possible to send with less worrying about thrown errors.

```js
// as default export
import structuredClone from '@ungap/structured-clone';
const cloned = structuredClone(
  {
    method() {
      // ignored, won't be cloned
    },
    special: Symbol('also ignored')
  },
  {
    // avoid throwing
    lossy: true,
    // avoid throwing *and* looks for toJSON
    json: true
  }
);
```

The behavior is the same found in *JSON* when it comes to *Array*, so that unsupported values will result as `null` placeholders instead.

#### toJSON

If `lossy` option is not enough, `json` will actually enforce `lossy` and also check for `toJSON` method when objects are parsed.

Alternative, the `json` exports combines all features:

```js
import {stringify, parse} from '@ungap/structured-clone/json';

parse(stringify({any: 'serializable'}));
```

---
_Source: https://npm.io/package/@ungap/structured-clone · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._