text: function duplicateCount(text) {
      text = text.toLowerCase();
      let obj = {}, cnt = 0;
      for (let el of text) {
          obj[el] = (obj[el] || 0) + 1;
      }
      for (let i in obj) {
          if (obj[i] > 1) { cnt++; }
      }
      return cnt;
  }