loop-for-in-enumerable-false.js

let obj = {};

Object.defineProperty(obj, 'a', {
  value: 1,
  enumerable: false
});

Object.defineProperty(obj, 'b', {
  value: 2,
  enumerable: false
});

console.log(obj.propertyIsEnumerable('a'));

for(let key in obj) {
  console.log(key);
}