toKatakana(str) {
    return [...str]
      .map((ch) =>
        ch > '\u3040' && ch < '\u3097'
          ? String.fromCharCode(ch.charCodeAt(0) - this.shiftToHiragana)
          : ch
      )
      .join('');
  }
Converts hiragana characters to katakana
@param {String} str Input string.