title: Does ES6 introduce a well-defined order of enumeration for object properties?
body: <p>Does ES6 introduce a well-defined order of enumeration for object properties?</p>
  
  <pre><code>var o = {
    '1': 1,
    'a': 2,
    'b': 3
  }
  
  Object.keys(o); // ["1", "a", "b"] - is this ordering guaranteed by ES6?
  
  for(let k in o) {
    console.log(k);
  } // 1 2 3 - is this ordering guaranteed by ES6?
  </code></pre>