Enumeration order incorrect with deletes

[bterlson]

let obj = {x: 1, y: 2};
obj.p1 = 1;
obj.p2 = 2;
delete obj.p1;
obj.p1 = 1;

let str = '';
for (prop in obj) {
    str += '<' + prop + '> ';
}

print(str);

┌─────────────────────┬───────────────────┐
│ Chakra              │ <x> <y> <p1> <p2> │
├─────────────────────┼───────────────────┤
│ JavaScriptCore      │ <x> <y> <p2> <p1> │
│ SpiderMonkey        │                   │
│ V8                  │                   │
└─────────────────────┴───────────────────┘

JSC, SM, and V8 have the proper behavior here. The spec requires that own properties are enumerated in order of creation. In the example above, p1 is the last property created and so should be last (the fact that it existed before is not relevant).

[VSadov]

possibly the same as #3505

[bakkot]

The spec does not actually require this (or any) order for for-in, though I would like it to and may try to get consensus on a normative change. But this is observable with for example Reflect.ownKeys, which uses OrdinaryOwnPropertyKeys directly without the "The mechanics and order of enumerating the properties is not specified" escape hatch present in EnumerateObjectProperties (which is what for-in uses).