npm package: @metowolf/json-bigint
Description: JSON.parse with bigints support
Author: metowolf
Latest version: 1.0.1

# json-bigint

JSON.parse/stringify with bigints support. Based on Douglas Crockford [JSON.js](https://github.com/douglascrockford/JSON-js) package and [bignumber.js](https://github.com/MikeMcl/bignumber.js) library.

Native `Bigint` was added to JS recently, so we added an option to leverage it instead of `bignumber.js`. However, the parsing with native `BigInt` is kept an option for backward compability.

While most JSON parsers assume numeric values have same precision restrictions as IEEE 754 double, JSON specification _does not_ say anything about number precision. Any floating point number in decimal (optionally scientific) notation is valid JSON value. It's a good idea to serialize values which might fall out of IEEE 754 integer precision as strings in your JSON api, but `{ "value" : 9223372036854775807}`, for example, is still a valid RFC4627 JSON string, and in most JS runtimes the result of `JSON.parse` is this object: `{ value: 9223372036854776000 }`

==========

example:

```js
var JSONbig = require('@metowolf/json-bigint');

var json = '{ "value" : 9223372036854775807, "v2": 123 }';
console.log('Input:', json);
console.log('');

console.log('node.js built-in JSON:');
var r = JSON.parse(json);
console.log('JSON.parse(input).value : ', r.value.toString());
console.log('JSON.stringify(JSON.parse(input)):', JSON.stringify(r));

console.log('\n\nbig number JSON:');
var r1 = JSONbig.parse(json);
console.log('JSONbig.parse(input).value : ', r1.value.toString());
console.log('JSONbig.stringify(JSONbig.parse(input)):', JSONbig.stringify(r1));
```

Output:

```
Input: { "value" : 9223372036854775807, "v2": 123 }

node.js built-in JSON:
JSON.parse(input).value :  9223372036854776000
JSON.stringify(JSON.parse(input)): {"value":9223372036854776000,"v2":123}


big number JSON:
JSONbig.parse(input).value :  9223372036854775807
JSONbig.stringify(JSONbig.parse(input)): {"value":9223372036854775807,"v2":123}
```

### Options

The behaviour of the parser is somewhat configurable through 'options'

#### options.strict, boolean, default false

Specifies the parsing should be "strict" towards reporting duplicate-keys in the parsed string.
The default follows what is allowed in standard json and resembles the behavior of JSON.parse, but overwrites any previous values with the last one assigned to the duplicate-key.

Setting options.strict = true will fail-fast on such duplicate-key occurances and thus warn you upfront of possible lost information.

example:

```js
var JSONbig = require('@metowolf/json-bigint');
var JSONstrict = require('@metowolf/json-bigint')({ strict: true });

var dupkeys = '{ "dupkey": "value 1", "dupkey": "value 2"}';
console.log('\n\nDuplicate Key test with both lenient and strict JSON parsing');
console.log('Input:', dupkeys);
var works = JSONbig.parse(dupkeys);
console.log('JSON.parse(dupkeys).dupkey: %s', works.dupkey);
var fails = 'will stay like this';
try {
  fails = JSONstrict.parse(dupkeys);
  console.log('ERROR!! Should never get here');
} catch (e) {
  console.log(
    'Succesfully catched expected exception on duplicate keys: %j',
    e
  );
}
```

Output

```
Duplicate Key test with big number JSON
Input: { "dupkey": "value 1", "dupkey": "value 2"}
JSON.parse(dupkeys).dupkey: value 2
Succesfully catched expected exception on duplicate keys: {"name":"SyntaxError","message":"Duplicate key \"dupkey\"","at":33,"text":"{ \"dupkey\": \"value 1\", \"dupkey\": \"value 2\"}"}

```

#### options.storeAsString, boolean, default false

Specifies if BigInts should be stored in the object as a string, rather than the default BigNumber.

Note that this is a dangerous behavior as it breaks the default functionality of being able to convert back-and-forth without data type changes (as this will convert all BigInts to be-and-stay strings).

example:

```js
var JSONbig = require('@metowolf/json-bigint');
var JSONbigString = require('@metowolf/json-bigint')({ storeAsString: true });
var key = '{ "key": 1234567890123456789 }';
console.log('\n\nStoring the BigInt as a string, instead of a BigNumber');
console.log('Input:', key);
var withInt = JSONbig.parse(key);
var withString = JSONbigString.parse(key);
console.log(
  'Default type: %s, With option type: %s',
  typeof withInt.key,
  typeof withString.key
);
```

Output

```
Storing the BigInt as a string, instead of a BigNumber
Input: { "key": 1234567890123456789 }
Default type: object, With option type: string

```

#### options.useNativeBigInt, boolean, default false

Specifies if parser uses native BigInt instead of bignumber.js

example:

```js
var JSONbig = require('@metowolf/json-bigint');
var JSONbigNative = require('@metowolf/json-bigint')({ useNativeBigInt: true });
var key = '{ "key": 993143214321423154315154321 }';
console.log(`\n\nStoring the Number as native BigInt, instead of a BigNumber`);
console.log('Input:', key);
var normal = JSONbig.parse(key);
var nativeBigInt = JSONbigNative.parse(key);
console.log(
  'Default type: %s, With option type: %s',
  typeof normal.key,
  typeof nativeBigInt.key
);
```

Output

```
Storing the Number as native BigInt, instead of a BigNumber
Input: { "key": 993143214321423154315154321 }
Default type: object, With option type: bigint

```

#### options.alwaysParseAsBig, boolean, default false

Specifies if all numbers should be stored as BigNumber.

Note that this is a dangerous behavior as it breaks the default functionality of being able to convert back-and-forth without data type changes (as this will convert all Number to be-and-stay BigNumber)

example:

```js
var JSONbig = require('@metowolf/json-bigint');
var JSONbigAlways = require('@metowolf/json-bigint')({ alwaysParseAsBig: true });
var key = '{ "key": 123 }'; // there is no need for BigNumber by default, but we're forcing it
console.log(`\n\nStoring the Number as a BigNumber, instead of a Number`);
console.log('Input:', key);
var normal = JSONbig.parse(key);
var always = JSONbigAlways.parse(key);
console.log(
  'Default type: %s, With option type: %s',
  typeof normal.key,
  typeof always.key
);
```

Output

```
Storing the Number as a BigNumber, instead of a Number
Input: { "key": 123 }
Default type: number, With option type: object

```

If you want to force all numbers to be parsed as native `BigInt`
(you probably do! Otherwise any calulations become a real headache):

```js
var JSONbig = require('@metowolf/json-bigint')({
  alwaysParseAsBig: true,
  useNativeBigInt: true,
});
```

#### options.protoAction, boolean, default: "error". Possible values: "error", "ignore", "preserve"

#### options.constructorAction, boolean, default: "error". Possible values: "error", "ignore", "preserve"

Controls how `__proto__` and `constructor` properties are treated. If set to "error" they are not allowed and
parse() call will throw an error. If set to "ignore" the prroperty and it;s value is skipped from parsing and object building.
If set to "preserve" the `__proto__` property is set. One should be extra careful and make sure any other library consuming generated data
is not vulnerable to prototype poisoning attacks.

example:

```js
var JSONbigAlways = require('@metowolf/json-bigint')({ protoAction: 'ignore' });
const user = JSONbig.parse('{ "__proto__": { "admin": true }, "id": 12345 }');
// => result is { id: 12345 }
```

### Links:

- [RFC4627: The application/json Media Type for JavaScript Object Notation (JSON)](http://www.ietf.org/rfc/rfc4627.txt)
- [Re: \[Json\] Limitations on number size?](http://www.ietf.org/mail-archive/web/json/current/msg00297.html)
- [Is there any proper way to parse JSON with large numbers? (long, bigint, int64)](http://stackoverflow.com/questions/18755125/node-js-is-there-any-proper-way-to-parse-json-with-large-numbers-long-bigint)
- [What is JavaScript's Max Int? What's the highest Integer value a Number can go to without losing precision?](http://stackoverflow.com/questions/307179/what-is-javascripts-max-int-whats-the-highest-integer-value-a-number-can-go-t)
- [Large numbers erroneously rounded in Javascript](http://stackoverflow.com/questions/1379934/large-numbers-erroneously-rounded-in-javascript)

### Note on native BigInt support

#### Stringifying

Full support out-of-the-box, stringifies BigInts as pure numbers (no quotes, no `n`)

#### Limitations

- Roundtrip operations

`s === JSONbig.stringify(JSONbig.parse(s))` but

`o !== JSONbig.parse(JSONbig.stringify(o))`

when `o` has a value with something like `123n`.

`JSONbig` stringify `123n` as `123`, which becomes `number` (aka `123` not `123n`) by default when being reparsed.

There is currently no consistent way to deal with this issue, so we decided to leave it, handling this specific case is then up to users.