Parent/Child class hierachy in nodejs - node.js

Question

child.js
class Child {
constructor(){
this.helloWorld = "Hello World";
}
run() {
}
}
export default new Child();
parent.js
import child from './child.js';
class Parent {
constructor() {
this.child = child;
}
}
export default new Parent();
index.js
import parent from './parent.js'
console.log(parent.child.helloWorld); <-- does not throws an error, displays "Hello World"
console.log(parent.child.run); <-- throws an error (Cannot read property run from undefined)
console.log(parent.child.run()); <-- throws an error (Cannot read property run from undefined)
If I do console.log(parent.child) in index.js, run does not show up, however the property helloWorld does..
How can I have the functions exposed as well? I was hoping to be able to do this to help keep my code a bit more organized, so was going to separate it out into separate classes to help minimize the amount of code in each file.

Answer 1

To make one thing clear from the start: The error you seem to get has nothing to do with run not appearing in the console.log output.
If your code really throws that error then that means that the value of parent.child is undefined. Hence when you call console.log(parent.child), you should see undefined, not an object. However, I don't see why you'd get that error.
Anyways, run is defined on the prototype of parent.child, not on itself. console.log most likely shows an object's own properties (the console API is not standardized, so results can vary between environments). That's normal.
Simple example to reproduce:
var foo = {
x: 42
};
var bar = Object.create(foo);
bar.y = 21;
console.log(bar, bar.x, bar.y);
// Open the browser console to see output
bar.x is accessible even though console.log doesn't show it (in Chrome at least).

Answer 2

Well I'm not sure if helps you to solve the problem, but whenever I want to add inheritance, I use extends and super here is an example:
Base Class:
class BaseDataModel {
constructor() {
}
getModel() {
return 'model';
}
module.exports.BaseDataModel = BaseDataModel;
Class extending Base Class:
"use strict"
// Imports
const BaseDataModel = require('../baseDataModel').BaseDataModel; // use the proper location
class UserMembershipModel extends BaseDataModel {
constructor() {
super(); // this is optional, I use this to inherit the constructors
}
getChildModel() {
return super.getModel(); // This is how you access the function from your extended class
}
module.exports.UserMembershipModel = UserMembershipModel;
Again, not sure if it solves your problem, since your actually adding a property with a Child class. My example is actually extending (or UserMembershipModel inherits from BaseDataModel).
Hope this helps you a bit.