Question 382784 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Passing the Class Variables from one class to another

I have two classes, A and B. I will only be setting the values of class A and I want class B variables to hold the same value as class A or have have access to all values of class A variables. In my case, class A and B should not be inherited logically. Is this possible without inheritance?.

In the below code, I have given an example where I need the value of only one variable and I could have passed the name as a method param. But, in my actual project I need to set the value of 20+ variables and it is not easy to pass around 20+ values to another class.

class B {
  name: string
  age: number

  print() {
    console.log(this.name);
  }
}

const b = new B();

class A {
  name: string;
  age: number;

  printValues() {
    b.print()
  }
}

const a = new A();
a.name = "TOM"
a.printValues() // Want to Print TOM
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2

Answers


  1. 0

    A should have a property that links it to a B instance. Then you can use a setter to pass the name assignment through.

    class B {
  name: string
  age: number

  print() {
    console.log(this.name);
  }
}

const b = new B();

class A {
  age: number;
  b: B;

  constructor(b) {
    this.b = b;
  }

  get name() {
    return this.b.name;
  };

  set name(new_name) {
    this.b.name = new_name;
  }

  printValues() {
    this.b.print()
  }
}

const a = new A(b);
a.name = "TOM"
a.printValues() // Want to Print TOM
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  2. 0

    You can simultaneously assign values to both instances with Proxy:

    class B{
  print() {
    Object.entries(this).forEach(([k,v]) => console.log(k, ':', v));
  }
}

const b = new B();

class A {
  constructor(b){
    return new Proxy(this, {
      set(_, prop, val, proxy){
        b[prop] = val;
        return Reflect.set(...arguments);
      }
    });
  }
  printValues() {
    b.print()
  }
}

const a = new A(b);

a.name = "TOM";
a.age = 33;
a.printValues() // Want to Print TOM

    But better save b in the a instance with the A’s constructor argument or create b in the A’s constructor.

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