Enumeration order was indeed (finally) added to the ES2015 spec. Here&#x27;s a link to the release candidate spec for the [[OwnPropertyKeys]] algorithm:<p><a href="https:&#x2F;&#x2F;people.mozilla.org&#x2F;~jorendorff&#x2F;es6-draft.html#sec-ordinary-object-internal-methods-and-internal-slots-ownpropertykeys" rel="nofollow">https:&#x2F;&#x2F;people.mozilla.org&#x2F;~jorendorff&#x2F;es6-draft.html#sec-or...</a>