es6-json-stable-stringify

Deterministic JSON.stringify() - a faster version of @substack's json-stable-strigify written in ES6. By deterministic we mean stable result for the same source across different iterations and platforms. The reason why it could be helpful even with modern Node is that by passing custom replacer as JSON.stringify argument you still cannot override Object keys iteration order which will result to

{"1":1,"2":2,"11":11}

instead of

{"1":1,"11":11,"2":2}

You can also pass a custom comparison and replacer functions and use your favorite indentation if you have to pretty print the output.

Example

const stringify = require('es6-json-stable-stringify');
const obj = { c: 8, b: [{ z: 6, y: 5, x: 4 }, 7], a: 3 };
console.log(stringify(obj));

output:

{"a":3,"b":[{"x":4,"y":5,"z":6},7],"c":8}

Methods

const stringify = require('es6-json-stable-stringify')
const str = stringify(obj)

Return a deterministic stringified string str from the object obj.

Options

space

Gives an ability to prettify output. Space is expected to be of string type, default value is empty string. The most commonly used indentation is two spaces:

const stringify = require('es6-json-stable-stringify');
 
const options = { space: '  ' };
const s = stringify(obj, options);
 
console.log(s);

which results in prettified output string:

{
  "a": 3,
  "b": [
    {
      "x": 4,
      "y": 5,
      "z": 6,
    },
    7
  ],
  "c": 8
}

comparator

If options is given, you can supply an options.comparator to have a custom comparison function for object keys. Your function options.comparator is called with these parameters:

comparator({ key: akey, value: avalue }, { key: bkey, value: bvalue })

For example, to sort on the object key names in reverse order you could write:

const stringify = require('es6-json-stable-stringify');
 
const obj = { c: 8, b: [{ z: 6, y: 5, x: 4 }, 7], a: 3 };
const options = { comparator: (a, b) => a.key < b.key ? 1 : -1 };
const s = stringify(obj, options);
console.log(s);

which results in the output string:

{"c":8,"b":[{"z":6,"y":5,"x":4},7],"a":3}

Or if you wanted to sort on the object values in reverse order, you could write:

const stringify = require('es6-json-stable-stringify');
 
const obj = { d: 6, c: 5, b: [{ z: 3, y: 2, x: 1 }, 9], a: 10 };
const s = stringify(obj, (a, b) => a.value < b.value ? 1 : -1);
console.log(s);

which outputs:

{"d":6,"c":5,"b":[{"z":3,"y":2,"x":1},9],"a":10}

replacer

The replacer parameter is a function options.replacer(key, value) that behaves the same as the replacer from the core JSON object.

const stringify = require('es6-json-stable-stringify');
 
const obj = { a: { c: 1 }, b: 2, c: 3 };
// Replacer which filters nodes with key equal to 'c'
const replacer = (name, value) => name === 'c' ? undefined : value;
const s = stringify(obj, { ...options, replacer });
console.log(s);

which outputs:

{"a":{},"b":2} 

cycles

Pass true in opts.cycles to stringify circular property as __cycle__ - the result will not be a valid JSON string in this case.

TypeError will be thrown in case of circular object without this option.

Install

With npm do:

npm install es6-json-stable-stringify

Benchmarks

To run benchmark (requires Node.js 10+):

node benchmark

Results:

fast-json-stable-stringify x 55.21 ops/sec ±2.98% (58 runs sampled)
es6-json-stable-stringify x 63.52 ops/sec ±1.71% (66 runs sampled)
json-stable-stringify x 48.94 ops/sec ±2.46% (64 runs sampled)
fast-stable-stringify x 67.05 ops/sec ±2.17% (68 runs sampled)
faster-stable-stringify x 58.41 ops/sec ±2.37% (61 runs sampled)
The fastest is fast-stable-stringify

Although "fast-stable-stringify" is actually slightly faster, it does not support nor pretty printed JSON output nor replacer functions.

License

MIT