Nope, they should be iterated in their defined order: https://tc39.github.io/ecma262/#sec-ordinaryownpropertykeys https://tc39.github.io/ecma262/#sec-ordinaryow

Nope, they should be iterated in their defined order: https://tc39.github.io/ecma262/#sec-ordinaryownpropertykeys https://tc39.github.io/ecma262/#sec-ordinaryownpropertykeys I think they added this with ES2015.