对象构建未按预期工作

Question

I have 3 different classes A, B, C.

A is, essentially, the parent of both B and C. When building both B and C object, A has to be included too.

Eventually, the class returns an object, which is currently B (inherits A), or C (inherits A), or just A.

Initialising of new object: const A = new A("a", "b", "c").json(); or const C = new C("a", "b", "c", "cClass1", "cClass2").json();

At the moment, I use inheritance to achieve this:

export class A {
  constructor (option1, option2, option3) {
    this.option1 = option1;
    this.option2 = option2;
    this.option3 = option3;
  }

  json () {
    return {
      key1: this.option1,
      key2: this.option2,
      key3: this.option3,
    };
  }
}

export class B extends A {
  constructor (option1, option2, option3, bClass1, bClass2) {
    super(option1, option2, option3);
    this.bClassKey1 = bClass1;
    this.bClassKey2 = bClass2;
  }

  json () {
    return {
      ...super.json(),
      bClassKey1: this.bClass1,
      bClassKey2: this.bClass2
    };
  }
}

export class C extends A {
  constructor (option1, option2, option3, cClass1, cClass2) {
    super(option1, option2, option3);
    this.cClassKey1 = cClass1;
    this.cClassKey2 = cClass2;
  }

  json () {
    return {
      ...super.json(),
      cClassKey1: this.cClass1,
      cClassKey2: this.cClass2
    };
  }
}

I now need to change how the objects are built, because I need to achieve the following:

I need an object that contains all of the classes unique parameters, like so:

{
    key1: option1,
    key2: option2,
    key3: option3,
    bClassKey1: bClass1,
    bClassKey2: bClass2,
    cClassKey1: cClass1,
    cClassKey2: cClass2
}

However, I cannot use multiple inheritance in JS (apart from mixin NPM, but I'd rather attempt to achieve it natively).

How can I return a object, that's built with A parameters, B parameters (without A) and C parameters (without A). However, there's still situations where B and C need to be built, that extends the parent of A.

Answer 1

It sounds like you want to use aggregation rather than inheritance. Then, each of the classes would have a method that added its information to an object, and you'd use any combination of those methods you wanted.

 /*export*/ class A { constructor (option1, option2, option3) { this.option1 = option1; this.option2 = option2; this.option3 = option3; } json (target = {}) { // Could also use Object.assign here if **all** enumerable properties are desired target.key1 = this.option1; target.key2 = this.option2; target.key3 = this.option3; return target; } } /*export*/ class B { constructor (bClass1, bClass2) { this.bClassKey1 = bClass1; this.bClassKey2 = bClass2; } json (target = {}) { // Could also use Object.assign here if **all** enumerable properties are desired // (Duplicating the names introduces the opportunity of error, which in fact // there was in the question) target.bClassKey1 = this.bClassKey1; target.bClassKey2 = this.bClassKey2; return target; } } /*export*/ class C { constructor (cClass1, cClass2) { this.cClassKey1 = cClass1; this.cClassKey2 = cClass2; } json (target = {}) { // Could also use Object.assign here if **all** enumerable properties are desired // (Duplicating the names introduces the opportunity of error, which in fact // there was in the question) target.cClassKey1 = this.cClassKey1; target.cClassKey2 = this.cClassKey2; return target; } } const a = new A("option1value", "option2value", "option3value"); const b = new B("bClass1value", "bClass2value"); const c = new C("cClass1value", "cClass2value"); const o = c.json(b.json(a.json())); /* Or, but it requires more temporary objects: const o = {...a.json(), ...b.json(), ...c.json()}; */ console.log(o);