Функции работы с ключами

const hasKey = (obj, keys) => {
  return (
    keys.length > 0 &&
    keys.every(key => {
      if (typeof obj !== 'object' || !obj.hasOwnProperty(key)) return false;
      obj = obj[key];
      return true;
    })
  );
};

let obj = {
  a: 1,
  b: { c: 4 },
  'b.d': 5
};
hasKey(obj, ['a']); // true
hasKey(obj, ['b']); // true
hasKey(obj, ['b', 'c']); // true
hasKey(obj, ['b.d']); // true
hasKey(obj, ['d']); // false
hasKey(obj, ['c']); // false
hasKey(obj, ['b', 'f']); // false

const assertValidKeys = (obj, keys) =>
  Object.keys(obj).every(key => keys.includes(key));

assertValidKeys({ id: 10, name: 'apple' }, ['id', 'name']); // true
assertValidKeys({ id: 10, name: 'apple' }, ['id', 'type']); // false

const symbolizeKeys = obj =>
  Object.keys(obj).reduce(
    (acc, key) => ({ …acc, [Symbol(key)]: obj[key] }),
    {}
  );

symbolizeKeys({ id: 10, name: 'apple' });
// { [Symbol(id)]: 10, [Symbol(name)]: 'apple' }

const findKeys = (obj, val) =>
  Object.keys(obj).filter(key => obj[key] === val);

const ages = {
  Leo: 20,
  Zoey: 21,
  Jane: 20,
};
findKeys(ages, 20); // [ 'Leo', 'Jane' ]

const commonKeys = (obj1, obj2) =>
  Object.keys(obj1).filter(key => obj2.hasOwnProperty(key));

commonKeys({ a: 1, b: 2 }, { a: 2, c: 1 }); // ['a']

const pick = (obj, arr) =>
  arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});

pick({ a: 1, b: '2', c: 3 }, ['a', 'c']); // { 'a': 1, 'c': 3 }

const findLastKey = (obj, fn) =>
  Object.keys(obj)
    .reverse()
    .find(key => fn(obj[key], key, obj));

findLastKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true }
  },
  x => x['active']
); // 'pebbles'

const findKey = (obj, fn) =>
  Object.keys(obj).find(key => fn(obj[key], key, obj));

findKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true }
  },
  x => x['active']
); // 'barney'

const obj = { a: 1 };
obj.b = 2;
obj.c = 3;
// obj = { a: 1, b: 2, c: 3 }

const obj = { a: 1 };
const bKey = 'b';
obj[bKey] = 2;
obj['c'] = 3;
// obj = { a: 1, b: 2, c: 3 }

const obj = { a: 1 };
Object.assign(obj, { b: 2 }, { c: 3 });
// obj = { a: 1, b: 2, c: 3 }

const obj = { a: 1 };
Object.defineProperty(obj, 'b', {
  value: 2,
  enumerable: true,
  configurable: true,
  writable: true
});
Object.defineProperty(obj, 'c', {
  value: 3,
  enumerable: true,
  configurable: true,
  writable: true
});
// obj = { a: 1, b: 2, c: 3 }

const obj = { a: 1 };
const newObj = { …obj, b: 2, c: 3 };
// obj = { a: 1 }
// newObj = { a: 1, b: 2, c: 3 }