const myPreCondition = {
	a : { d : 1 },
	b : { e : 2, f : 3, g: 7 },
	c : 2
};

// then we might be able
const extra = myPreCondition.{ a, c };

// having the following
console.log(Object.keys(extra)); // ['a', 'c']
console.log(extra); // { a : { d : 1 }, c : 2 }

const deepExtra = myPreCondition.{ a, c, b.{e} },
console.log(Object.keys(deepExtra)); // ['a', 'c', 'e']

const otherExtra = myPreCondition.{ a, b.{ ... } },
console.log(Object.keys(deepExtra)); // ['a', 'e', 'f', 'g']
console.log(deepExtra); // { a : { d : 1}, e : 2, f : 3, g : 7 } 

const existentObject = { e : 1, f : 2 };

// so here is an **assignment**
existentObject.{ ...myPreCondition.{ c, b.{e, f} } };

console.log(Object.keys(existentObject)); // ['c', 'e', 'f']
console.log(existentObject.e); // 2, as it was at myPreCondition.b.e;
console.log(existentObject.f); // 3, as it was at myPreCondition.b.f;