hasKeys

interface Test {
  a?: {
    b?: {
      c?: string;
    };
  } | null;
  x?: number | null;
}

const obj: Test = { a: { b: { c: 'hello' } }, x: 42 };

if (hasKeys(obj, ['a.b.c', 'x'])) {
  // Here, obj is narrowed to:
  // {
  //   a: { b: { c: string } };
  //   x: number;
  // }
  console.log(obj.a.b.c.toUpperCase());
  console.log(obj.x.toFixed(2));
}