# flatted
> A super light and fast circular JSON parser.
Latest version **3.4.4** (published 2026-07-30) · ISC license · 0 weekly downloads
## Install
```sh
npm install flatted
pnpm add flatted
yarn add flatted
bun add flatted
```
## Health
**Score 70/100 (B)** — status: active.
Positive: has types; esm support; no vulnerabilities; recently updated; high maintenance score; high quality score.
Warnings: low downloads.
## Facts
| | |
|---|---|
| Version | 3.4.4 |
| Published | 2026-07-30 |
| First published | 2018-04-26 |
| Weekly downloads | 0 |
| License | ISC |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Dependencies | 0 |
| Unpacked size | 37.6 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 1157 |
| Author | Andrea Giammarchi |
| Maintainers | webreflection |
| Keywords | circular, JSON, fast, parser, minimal |
## Links
- npm: https://www.npmjs.com/package/flatted
- Repository: https://github.com/WebReflection/flatted
- Homepage: https://github.com/WebReflection/flatted#readme
- Issues: https://github.com/WebReflection/flatted/issues
- npm.io page: https://npm.io/package/flatted
## Alternatives
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## Recent versions
- 3.4.4 (latest) — 2026-07-30
- 3.4.3 — 2026-07-22
- 3.4.2 — 2026-03-17
- 3.4.1 — 2026-03-09
- 3.4.0 — 2026-03-08
- 3.3.4 — 2026-03-02
- 3.3.3 — 2025-02-18
- 3.3.2 — 2024-11-18
- 3.3.1 — 2024-02-21
- 3.3.0 — 2024-02-20
- 3.2.13 — 2024-02-20
- 3.2.12 — 2024-02-20
- 3.2.11 — 2024-02-20
- 3.2.10 — 2024-02-20
- 3.2.9 — 2023-09-16
- … 29 more at https://npm.io/package/flatted/versions
## README
# flatted
[](https://www.npmjs.com/package/flatted) [](https://coveralls.io/github/WebReflection/flatted?branch=main) [](https://opensource.org/licenses/ISC) 
**Social Media Photo by [Matt Seymour](https://unsplash.com/@mattseymour) on [Unsplash](https://unsplash.com/)**
A super light (0.5K) and fast circular JSON parser, directly from the creator of [CircularJSON](https://github.com/WebReflection/circular-json/#circularjson).
Available also for **[PHP](./php/flatted.php)**.
Available also for **[Python](./python/flatted.py)**.
Available also for **[Go](./golang/README.md)**.
- - -
## ℹ️ JSON only values
If you need anything more complex than values JSON understands, there is a standard approach to recursion and more data-types than what JSON allows, and it's part of the [Structured Clone polyfill](https://github.com/ungap/structured-clone/#readme).
- - -
```js
npm i flatted
```
Usable via [CDN](https://unpkg.com/flatted) or as regular module.
```js
// ESM
import {parse, stringify, toJSON, fromJSON} from 'flatted';
// CJS
const {parse, stringify, toJSON, fromJSON} = require('flatted');
const a = [{}];
a[0].a = a;
a.push(a);
stringify(a); // [["1","0"],{"a":"0"}]
```
## toJSON and fromJSON
If you'd like to implicitly survive JSON serialization, these two helpers helps:
```js
import {toJSON, fromJSON} from 'flatted';
class RecursiveMap extends Map {
static fromJSON(any) {
return new this(fromJSON(any));
}
toJSON() {
return toJSON([...this.entries()]);
}
}
const recursive = new RecursiveMap;
const same = {};
same.same = same;
recursive.set('same', same);
const asString = JSON.stringify(recursive);
const asMap = RecursiveMap.fromJSON(JSON.parse(asString));
asMap.get('same') === asMap.get('same').same;
// true
```
## Flatted VS JSON
As it is for every other specialized format capable of serializing and deserializing circular data, you should never `JSON.parse(Flatted.stringify(data))`, and you should never `Flatted.parse(JSON.stringify(data))`.
The only way this could work is to `Flatted.parse(Flatted.stringify(data))`, as it is also for _CircularJSON_ or any other, otherwise there's no granted data integrity.
Also please note this project serializes and deserializes only data compatible with JSON, so that sockets, or anything else with internal classes different from those allowed by JSON standard, won't be serialized and unserialized as expected.
### New in V1: Exact same JSON API
* Added a [reviver](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse#Syntax) parameter to `.parse(string, reviver)` and revive your own objects.
* Added a [replacer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#Syntax) and a `space` parameter to `.stringify(object, replacer, space)` for feature parity with JSON signature.
### Compatibility
All ECMAScript engines compatible with `Map`, `Set`, `Object.keys`, and `Array.prototype.reduce` will work, even if polyfilled.
### How does it work ?
While stringifying, all Objects, including Arrays, and strings, are flattened out and replaced as unique index. `*`
Once parsed, all indexes will be replaced through the flattened collection.
`*` represented as string to avoid conflicts with numbers
```js
// logic example
var a = [{one: 1}, {two: '2'}];
a[0].a = a;
// a is the main object, will be at index '0'
// {one: 1} is the second object, index '1'
// {two: '2'} the third, in '2', and it has a string
// which will be found at index '3'
Flatted.stringify(a);
// [["1","2"],{"one":1,"a":"0"},{"two":"3"},"2"]
// a[one,two] {one: 1, a} {two: '2'} '2'
```
---
_Source: https://npm.io/package/flatted · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._