AbstractAnimal.js

export default class AbstractAnimal {

    constructor(ModelClass) {

        if (!ModelClass) {
            throw new Error('Model is required to get the config obj');
        }

        this.config = {
            type: '',
            noise: ''
        };

        Object.assign(this.config, ModelClass.prototype.config);
        this.ModelClass = ModelClass;

    }


    say() {
        if (!this.config.noise)
            throw new Error("No one knows this sound");

        return this.config.noise;
    }

    sleepySay() {
        return new Promise((resolve, reject) => {
            if (!this.config.noise)
                throw new Error("No one knows this sound");

            resolve(this.config.noise);
        });
    }

}

Dog.js

import AbstractAnimal from './AbstractAnimal';

export class DogModel {
    constructor () {
        this.config = {
            type: 'dog',
            noise: 'woof'
        }
    }
}

export default class Dog extends AbstractAnimal {

    constructor() {
        super(DogModel);

        Object.assign(this, DogModel.prototype.config)
    }

    say() {
        return super.say();
    }

    sleepySay() {
        return super.sleepySay();
    }
}

Fox.js

import AbstractAnimal from './AbstractAnimal';

export class FoxModel {
    constructor () {
        this.config = {
            type: 'fox',
            noise: null
        }
    }
}

export default class Fox extends AbstractAnimal {

    constructor() {
        super(FoxModel);

        Object.assign(this, FoxModel.prototype.config)
    }

    say() {
        super.say();
    }

    sleepySay() {
        return super.sleepySay();
    }
}