Nested class in javascript, inheritance of private methods

Question

i'm quite a newbie in javascript, and i'm spending some time trying to create namespaced objects in js.

Now, that's what i'm trying to do:

MainObject = function() {

    var privateVariable = "i'm private";

    var privateMethod = function() {
        // doSomething
    }

    this.publicMethod = function() {
        // doPublicSomething
    }
}

MainObject.prototype.nested = function() {

    this.publicNestedMethod = function() {

        // that's not working at all
        this.privateMethod(privateVariable);

    }
}

MyObject = new MainObject();

MyObject.publicMethod();
MyObject.publicNestedMethod();

I tried to include the nested class inside the first one, but it's not working also if i try:

this.nested = function() {

    var mainObject = this;

    return {
        publicNestedMethod = function() {
            mainObject.privateMethod();             
        }   
    }
}();

Someone can help me please? i'm gonna loose my mind on this.

Phaedra.

Answer 1

JavaScript Classes and Inheritance (ES6)

According to ES6, you can use JavaScript classes and inheritance to accomplish what you need.

JavaScript classes, introduced in ECMAScript 2015, are primarily syntactical sugar over JavaScript's existing prototype-based inheritance.

Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes

I'm showing the examples below with variables, but it can be applied also to functions.

---

Inheritance (1st Approach)

This solution can only be used with getters for your private variables, otherwise your subclass will not get access to them.

class Main {
  constructor() {
    let privateVariable = "private";
    this.publicVariable = "public";

    this.getPrivateVariable = () => {
      return privateVariable;
    }
  }
}

Main.Sub = class Sub extends Main {
  getAllVariables() {
    return this.publicVariable + "-" + this.getPrivateVariable();
  }
}

// Testing...

let main = new Main();
let sub = new Main.Sub();

console.log(main.privateVariable); // undefined
console.log(main.publicVariable); // "public"

console.log(sub.privateVariable); // undefined
console.log(sub.publicVariable); // "public"

console.log(main.getPrivateVariable()); // "private"
console.log(sub.getPrivateVariable()); // "private"
console.log(sub.getAllVariables()) // "public-private"

Nesting (2nd Approach)

Maybe this solution is better for you because it doesn't expose your private variables outside the Main and Nested classes.

class Main {
  constructor() {
    let privateVariable = "private";
    this.publicVariable = "public";
    
    Main.Nested = class Nested extends Main {
      getAllVariables() {
        return this.publicVariable + "-" + privateVariable;
      }
    }
  }
}

// Testing...

let main = new Main();
let nested = new Main.Nested();

console.log(main.privateVariable); // undefined
console.log(main.publicVariable); // "public"

console.log(nested.privateVariable); // undefined
console.log(nested.publicVariable); // "public"

console.log(main.getPrivateVariable); // undefined
console.log(nested.getPrivateVariable); // undefined
console.log(nested.getAllVariables()) // "public-private"