oop - Find all classes in a Javascript application that extend a base class

Question

I have code like this

class Animal{}
class Dog extends Animal {}
class Cat extends Animal {}
class Donkey extends Animal {}

I want to look at all of the classes in my application's universe, and when I find one that descends from Animal, I want to create a new object of that type and add it to the list. This allows me to add functionality without having to update a list of things. So I can avoid the following:

var animals = [];
animals.push( new Dog() );
animals.push( new Cat() );
animals.push( new Donkey() );

PS: I don't want to add extra functionality to my classes or call them explicitly.

Answer 1

I think you could make use of decorators. For instance, you could create @Extends() one and provide base class as an argument, e.g. @Extends(Animal). Inside the decorator function, you could take the name of the class decorated with @Extends and and put it into an array or an object. Don't know if it is applicable in browsers, but it should be. In Node with TypeScript I would do something like:

import { MyClassMetadata } from './';

export function Extends(parent): (...args: any[]) => void {
    return (target: object): void => {
        MyClassMetadata.someVariableToStoreChildren[parent.constructor.name].push(
            target,
        );
    }
}

Then you can access the MyClassMetadata variable that stores array of children of a given class and use it the way you want. You can play with it and get the desired result.