Array.from.js

let cats = {
  '@@iterator': function () {
    let names = Object.keys(this), i = 0 
    return { 
      next: () => i < names.length ? { value: names[i++] } : { done: true }
    }
  },
  a: 1,
  b: 2,
  c: 3,
};
console.log(Array.from(cats));