function Rat(name) {
    this.name = name;
    this.unitedRats = [];

    Rat.prototype.unite = (rat) => {
        if (!(rat instanceof Rat)) {
            return;
        }

        this.unitedRats.push(rat);
    };

    Rat.prototype.getRats = () => this.unitedRats;

    Rat.prototype.toString = () => `${this.name}${this.unitedRats.map((r) => `\n##${r.name}`).join('')}`;
}

let firstRat = new Rat('Peter');
console.log(firstRat.toString()); // Peter

console.log(firstRat.getRats()); // []

firstRat.unite(new Rat('George'));
firstRat.unite(new Rat('Alex'));
console.log(firstRat.getRats());
// [ Rat { name: 'George', unitedRats: [] },
//  Rat { name: 'Alex', unitedRats: [] } ]

console.log(firstRat.toString());
// Peter
// ##George
// ##Alex