Is JSON.stringify() deterministic in V8?

Question

I\'ve not seen (yet?) JSON.stringify to be non-deterministic in Node.JS.

There is no guarantee it to be deterministic on the specification level.

Answer 1

In case anyone would look for a function that'll make the JSON dump predictable, I wrote one:

const sortObj = (obj) => (
  obj === null || typeof obj !== 'object'
  ? obj
  : Array.isArray(obj)
  ? obj.map(sortObj)
  : Object.assign({}, 
      ...Object.entries(obj)
        .sort(([keyA], [keyB]) => keyA.localeCompare(keyB))
        .map(([k, v]) => ({ [k]: sortObj(v) }),
    ))
);

Here's a composed deterministic JSON dump:

const deterministicStrigify = obj => JSON.stringify(deterministic(sortObj))

It works well with the examples above:

> obj1 = {};
> obj1.b = 5;
> obj1.a = 15;

> obj2 = {};
> obj2.a = 15;
> obj2.b = 5;

> deterministicStrigify(obj1)
'{"a":15,"b":5}'
> deterministicStrigify(obj2)
'{"a":15,"b":5}'
> JSON.stringify(obj1)
'{"b":5,"a":15}'
> JSON.stringify(obj2)
'{"a":15,"b":5}'