[рони]

TrumpTower,

const cities = [];
        while (true) {
            let city = prompt('Введите город');
            if (!city) break;
            city = city.replace(/[ЪЬЫ]+$/ig, '');

            let includes = cities.includes(city);
            if (includes) {
                alert(`${city} такой город есть в списке`);
            } else {
                cities.push(city);
                alert(`${city} добавлен в список`);
            }
        }