javascript - Object.keys order for large numerical indexes?

Question

I have this test:

let obj = {
    "5555555555": 5,
    "4444444444": 4,
    "3333333333": 3,
    "2222222222": 2,
};
console.log(Object.keys(obj));

Answer 1

None of the major implementations had ever been in line with that particular ES6 specification. But note that exceptions were allowed in EcmaScript 2015-2019 (see this)

Concerning the described behaviour, see for instance the V8 bug report Issue 7874: Respect OrdinaryOwnPropertyKeys order.

While EcmaScript 2016, 2017 and 2018 specifications remained unchanged in this respect, it was decided to align EcmaScript2019 with reality. The section on [[OwnPropertyKeys]]() now reads:

2. For each own property key P of O that is an array index, in ascending numeric index order, do
   ? ? a. Add P as the last element of keys.

So reference is to array index, which has an unchanged definition (+0 ≤ i < 2³²?1).

This change occurred in pull request Normative: Use array indices instead of integer indices in OrdinaryOwnPropertyKeys. See also the comments and cross-references there.