JS: Reflect.ownKeys

New in JS2015.

Reflect.ownKeys(obj)

Return a Array of the object's keys. (including Symbol keys and non-enumerable keys.)

const jj = {
  "y": 3,
  [Symbol("x")]: 4,
};

// list all properties of a object
console.log(Reflect.ownKeys(jj));
// [ "y", Symbol(x) ]