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

To clarify jmrk's answer;

According to the spec, integer keys are serialized in numeric order and non-integer keys in chronological order of property creation, e.g.;

var o = {};
o[2] = 2;
o.a = 3;
o.b = 4;
o["1"] = 1;

assert(JSON.stringify(o)==='{"1":1,"2":2,"a":3,"b":4}');

Therefore following assertion is guaranteed to be true

if( obj1 === obj2 ) {
  assert(JSON.stringify(obj1) === JSON.stringify(obj2));
}

but two "deep equal" objects may be serialized into different strings;

var obj1 = {};
obj1["a"] = true;
obj1["b"] = true;
assert(JSON.stringify(obj1)==='{"a":true,"b":true}');

var obj2 = {};
obj2["b"] = true;
obj2["a"] = true;
assert(JSON.stringify(obj2)==='{"b":true,"a":true}');

Spec quote;

1. Let keys be a new empty List.

2. For each own property key P of O that is an integer index, in ascending numeric index order, do

   a. Add P as the last element of keys.

3. For each own property key P of O that is a String but is not an integer index, in ascending chronological order of property creation, do

   a. Add P as the last element of keys.

4. For each own property key P of O that is a Symbol, in ascending chronological order of property creation, do

   a. Add P as the last element of keys.

5. Return keys.

From https://tc39.github.io/ecma262/#sec-ordinaryownpropertykeys