JavaScript `for in` returns sorted elements

Question

I am curious, I noticed, when starting up for inon an object with number keys. It seems that the elements are sorted sequentially. Can anyone explain why this is?

const thing = {
  "2": "any",
  "8": "thing",
  "3": "here",
  "7": "x",
  "6": "xx",
  "1": "xxx"
};

for (var item in thing) {
  console.log(item);
}

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