docs: function at(index) {
  
      if (!this) {
          throw TypeError();
      }
  
      const str = '' + this,
          len = str.length;
  
      if (index >= len) {
          return;
      }
      if (index < 0) {
          index = len - index;
      }
  
      let i = 0;
      for (let item of str) {
          if (i === index) {
              return item;
          }
      }
  
      return;
  
  }