IVAN2

function solveClasses() {
    class Pet {
        constructor(owner, name) {
            this.owner = owner;
            this.name = name;
            this.comments = [];
        }

        addComment(comment) {
            this.comments.forEach(c => {
                if (c === comment) {
                    throw new Error('This comment is already added!');
                }
            });
            this.comments.push(comment);

            return 'Comment is added.';
        }

        feed() {
            return `${this.name} is fed`;
        }

        toString() {
            let result = `Here is ${this.owner}'s pet ${this.name}.`
            if (this.comments.length > 0) {
                result += `\nSpecial requirements: ${this.comments.join(', ')}`;
            }
            return result;
        }
    }

    class Cat extends Pet {
        constructor( owner, name, insideHabits, scratching ) {
            super(owner, name);
            this.insideHabits = insideHabits;
            this.scratching = scratching;
        }

        feed() {
            return super.feed() + ', happy and purring.';
        }

        toString() {
            let result = super.toString() + '\n' + `Main information:\n${this.name} is a cat with ${this.insideHabits}`;
            if (this.scratching) {
                result += ', but beware of scratches.';
            }
            return result;
        }
    }

    class Dog extends Pet {
        constructor(owner, name, runningNeeds, trainability) {
            super(owner, name);
            this.runningNeeds = runningNeeds;
            this.trainability = trainability;
        }

        feed() {
            return super.feed() + ', happy and wagging tail.';
        }

        toString() {
            let result = super.toString() + '\n' + 'Main information:\n';
            result += `${this.name} is a dog with need of ${this.runningNeeds}km running every day and ${this.trainability} trainability.`;
            return result;
        }
    }

    return {
        Pet,
        Cat,
        Dog
    }
}