[simonbw]

I believe in es6 Object literals are guaranteed to keep their ordering, and Object.keys() will iterate through them in the order defined.

[denpaDawn]

The ordering of Object.keys() is equal to insertion order of the keys into the object. So if you have an Object generation function, it can insert the keys in the proper order (and take advantage of stuff like v8 hidden classes)

http://2ality.com/2015/10/property-traversal-order-es6.html