For in loops

for-in.js

let grandparent = Object.create(Object.prototype, {
  foo: {
    enumerable: true,
    configurable: true,
    writable: true,
    value: "1"
  }
})
let parent = Object.create(grandparent, {
  foo: {
    enumerable: false,
    configurable: true,
    writable: true,
    value: "2"
  }
});

let obj = Object.create(parent);

for(let prop in obj) {
  console.log(prop, obj[prop]);
}