# flatted

Social Media Photo by Matt Seymour on Unsplash

## Announcement 📣

There is a standard approach to recursion and more data-types than what JSON allows, and it's part of the Structured Clone polyfill.

Beside acting as a polyfill, its `@ungap/structured-clone/json` export provides both `stringify` and `parse`, and it's been tested for being faster than flatted, but its produced output is also smaller than flatted in general.

The @ungap/structured-clone module is, in short, a drop in replacement for flatted, but it's not compatible with flatted specialized syntax.

However, if recursion, as well as more data-types, are what you are after, or interesting for your projects/use cases, consider switching to this new module whenever you can 👍

A super light (0.5K) and fast circular JSON parser, directly from the creator of CircularJSON.

Now available also for PHP.

    npm i flatted

Usable via CDN or as regular module.

    // 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:

    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 parameter to `.parse(string, reviver)` and revive your own objects.
- Added a replacer 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

    // 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'