text: function isIsogram(str) {
    if (str === "") return true;
    str = str.toLowerCase();
    let obj = {};
  
    for (let s of str) {
      obj[s] = (obj[s] || 0) + 1;
    }
  
    for (let i of Object.values(obj)) {
      if (i > 1) {
        return false;
      }
    }
    return true;
  }
  