class Sumator {
  constructor() {
    this.data = [];

    this.add(item) {
        this.data.push(item);
    }

    this.sumNums() {
        let sum = 0;
        for (let item of this.data)
            if (typeof (item) === 'number')
                sum += item;
        return sum;
    }

    this.removeByFilter(filterFunc) {
        this.data = this.data.filter(x => !filterFunc(x));
    }

    this.toString() {
        if (this.data.length > 0)
            return this.data.join(", ");
        else
            return '(empty)';
    }
  }
}