TypeScript icon, indicating that this package has built-in type declarations

0.0.8 • Public • Published

JSON22 - JSON with types

The JSON22 is a superset of JSON with an ability to serialize/deserialize classes and extended support for number variables.


To there ...

const value = {
    name: "Femistoclus",
    amount: 3873133n,
    debt: NaN,
    date: new Date('2022-01-07'),
const string = JSON22.stringify(value);
// =>
// {
//    "name": "Femistoclus"
//    "amount": 3873133n,
//    "debt": NaN,
//    "date": Date(1641513600000),
// }

... and back

const string = `{
  "name": "Femistoclus"
  "amount": 3873133n,
  "debt": NaN,
  "date": Date(1641513600000),
const value = JSON22.parse(string);
console.log(typeof value.date, value.date.constructor.name); // => object Date
console.log(typeof value.amount); // => bigint
console.log(typeof value.debt, isNaN(value.debt)); // => number true


  • Can parse standard JSON format
  • Support for BigInt values
  • Support for NaN values
  • Support for Infinity/-Infinity values
  • Support for typed serialization/deserialization, work with Date class out of the box
  • Allow using trailing commas
  • Zero-dependency npm-package
  • Both CJS/ESM modules support


npm install json22

In your code

import { JSON22 } from 'json22'

const data = { date: new Date() };
const s = JSON22.stringify(data);

For old-fashioned applications

const { JSON22 } = require('json22'); 

const data = { date: new Date() };
const s = JSON22.stringify(data);


Using with Express

There is library json22-express providing JSON22 support for expressjs applications

import express from 'express'; 
import { json22express } from 'json22-express'

const app = express();

app.get('/date', (req, res, next) => {
    res.status(200).json22({ date: new Date() });

Using with Axios

There is library json22-axios providing JSON22 support for client applications

import axios from 'axios';
import { Json22RequestInterceptor } from 'json22-axios';


async function geServerDate() {
  try {
      const resp = await axios.get('/date');
      return resp.data.date;
  } catch (e) {
  return null;


Note: JSON22 cannot be used as drop in JSON object replacement due to parse and stringify methods arguments incompatibility. But you may not be worried in case you are using first arguments only.

class JSON22 {
    static readonly mimeType: string;
    static parse<T>(text: string, options?: Json22ParseOptions): T;
    static stringify(value: any, options?: Json22StringifyOptions): string;

interface Json22ParseOptions {
    context?: Record<string, { new (...args: any) }>; // default { 'Date': Date }
    // To be extended

interface Json22StringifyOptions {
    // To be extended

JSON Extensions


With JSON22 you can use NaN, Infinity, -Infinity values. It means also this values will be stringified well in case it nested at an array or an object.

JSON.stringify([42, NaN, Infinity, -Infinity]); // => [42, null, null, null] 
JSON22.stringify([42, NaN, Infinity, -Infinity]); // => [42, NaN, Infinity, -Infinity]
JSON.stringify({ nan: NaN }); // => { "nan": null } 
JSON22.stringify({ nan: NaN }); // => { "nan": NaN }


JSON22 introduce support for BigInt values

JSON.stringify({ bigint: 123n }); // => Uncaught TypeError: Do not know how to serialize a BigInt
JSON22.stringify({ bigint: 123n }); // => { "bigint": 123n } 
JSON22.parse('{ "bigint": 123n }'); // => { bigint: 123n }

Trailing commas

It was not planned, but parser implementation work well with trailing commas. There is no sense to complicate the parser code to avoid it. It looks useful.

JSON.parse('[1, 2, 3, ]'); // => Uncaught SyntaxError: Unexpected token ] in JSON at position 9
JSON22.parse('[1, 2, 3, ]'); // => [1, 2, 3]
JSON.parse('{ "a": 1, "b": 2, "c": 3, }'); // => Uncaught SyntaxError: Unexpected token } in JSON at position 26
JSON22.parse('{ "a": 1, "b": 2, "c": 3, }'); // => { a: 1, b:2, c:3 }

Typed values

This is the most significant addition. It's allow you to serialize and deserialize any typed value. Out of the box it works well with date values.

const date = new Date('2022-01-07');
JSON.stringify(date); // => "2022-01-07T00:00:00.000Z"
JSON22.stringify(date); // => Date(1641513600000)
const date = JSON22.parse('Date(1641513600000)');
console.log(typeof date, date instanceof Date); // => object true 

This behavior is based on the valueOf method which is defined at the Object class. In case JSON22 find the valueOf method return a value which is not equal of the object itself then it will produce constructor literal. The valueOf of the Date class return numeric date representation. If you'll call the Date constructor with that value then date will be sort of 'restored'.

Custom valueOf implementation

To match this behavior you may implement you own valueOf method at you custom class.

Let's define a model class for demonstration

class TypedModel {
    constructor(data) {
        this.a = data?.a;
        this.b = data?.b;
    valueOf() {
        return { a: this.a, b: this.b };

That sort of classes will be serialised as typed objects

const value = new TypedModel({ a: 1, b: 2 });
JSON22.stringify(value); // => TypedModel({ "a": 1, "b": 1 }) 

The valueOf methods may return any serializable values, even typed objects

const value = new TypedModel({ a: 1, b: new Date('2022-01-07') });
JSON22.stringify(value); // => TypedModel({ "a": 1, "b": Date(1641513600000) }) 

Parsing context

Typically, serialization and deserialization are processes separated by different environments. Like serialization at a backend and deserialization at a frontend and vice versa. So TypedModel we defined above should be shared between environments. Also JSON22 parser should have a link to this class. In theory, we can push all such classes to a global scope. It is easy, however, it is not the best solution. It will produce global scope pollution, may cause naming conflicts, and it is not safe to allow parser to call any constructor from a global scope. That is why you should always pass deserialization context to parser.

const string = 'TypedModel({ "a": 1, "b": Date(1641513600000) })';
JSON22.parse(string); // => Error: Constructor TypedModel not defined in the context

const context = { 'TypedModel': TypedModel };
const value = JSON22.parse(string, { context });
console.log(value instanceof TypedModel); // => true

The valueOf method priority

The JSON22 support for toJSON method of an object as well as JSON. In some cases an object may have both valueOf and toJSON methods. Typical example is the Date class. The JSON22 at first is a solution to serialize/deserialize date values, so valueOf have higher priority over toJSON. This is also true for any object implementing valueOf and toJSON both.


JSON format is good enough for everyday usage. There are some libraries trying to introduce syntax to make JSON closer to modern JavaScript, some libraries trying to introduce functions serialization. All that is not important and is not required for everyday usage. However, there is one thing annoying me always - date values.

We are serializing dates a lot and each time we parse it back we are getting a string. As a result we have to deal with the Date constructor manually each time. Even if we are no need date as an object, date formatter will have to make date object in order to make user-friendly text representation. Otherwords we are forced to care about dates additionally. It produces bulky solutions or tons of inline type conversions.

But I'm lazy developer, I'll do everything to get rid of any additional careness.

Package Sidebar


npm i json22

Weekly Downloads






Unpacked Size

78.5 kB

Total Files


Last publish


  • dancecoder