【GAS】全角カタカナを半角に変換

/**
 * 全角カタカナを半角カタカナに変換する関数（正規表現 + 変換マップ方式）
 *
 * @param {string} str - 入力文字列
 *                         例: "アイウエオガギグゲゴ"
 * @returns {string} - 全角カタカナ部分が半角カタカナに変換された文字列
 *                         例: "ｱｲｳｴｵｶﾞｷﾞｸﾞｹﾞｺﾞ"
 *
 * 本関数は、VBAの StrConv(..., vbNarrow) に近い動作を
 * Google Apps Script 上で実現します。
 */
function convertZenKanaToHan(str) {
  // 入力が null や undefined の場合は、そのまま返す
  if (str == null) {
    return str;
  }

  // ▼ 正規表現の説明
  // [ァ-ヶー]+ は「全角カタカナの連続した文字列」を意味します。
  // ・ァ〜ヶ : カタカナの基本ブロック
  // ・ー      : 長音符
  // +        : 1文字以上の連続
  const regex = /[ァ-ヶー]+/g;

  // ▼ 全角→半角の対応表
  // 濁点・半濁点付き文字も、単独で対応を用意します。
  const zen = [
    "ガ","ギ","グ","ゲ","ゴ",
    "ザ","ジ","ズ","ゼ","ゾ",
    "ダ","ヂ","ヅ","デ","ド",
    "バ","ビ","ブ","ベ","ボ",
    "パ","ピ","プ","ペ","ポ",
    "ヴ", // 全角ヴ
    "ア","イ","ウ","エ","オ",
    "カ","キ","ク","ケ","コ",
    "サ","シ","ス","セ","ソ",
    "タ","チ","ツ","テ","ト",
    "ナ","ニ","ヌ","ネ","ノ",
    "ハ","ヒ","フ","ヘ","ホ",
    "マ","ミ","ム","メ","モ",
    "ヤ","ユ","ヨ",
    "ラ","リ","ル","レ","ロ",
    "ワ","ヲ","ン",
    "ァ","ィ","ゥ","ェ","ォ",
    "ャ","ュ","ョ","ッ",
    "ー"
  ];

  // 半角側の対応表（上記とインデックスで対応）
  const han = [
    "ｶﾞ","ｷﾞ","ｸﾞ","ｹﾞ","ｺﾞ",
    "ｻﾞ","ｼﾞ","ｽﾞ","ｾﾞ","ｿﾞ",
    "ﾀﾞ","ﾁﾞ","ﾂﾞ","ﾃﾞ","ﾄﾞ",
    "ﾊﾞ","ﾋﾞ","ﾌﾞ","ﾍﾞ","ﾎﾞ",
    "ﾊﾟ","ﾋﾟ","ﾌﾟ","ﾍﾟ","ﾎﾟ",
    "ｳﾞ",
    "ｱ","ｲ","ｳ","ｴ","ｵ",
    "ｶ","ｷ","ｸ","ｹ","ｺ",
    "ｻ","ｼ","ｽ","ｾ","ｿ",
    "ﾀ","ﾁ","ﾂ","ﾃ","ﾄ",
    "ﾅ","ﾆ","ﾇ","ﾈ","ﾉ",
    "ﾊ","ﾋ","ﾌ","ﾍ","ﾎ",
    "ﾏ","ﾐ","ﾑ","ﾒ","ﾓ",
    "ﾔ","ﾕ","ﾖ",
    "ﾗ","ﾘ","ﾙ","ﾚ","ﾛ",
    "ﾜ","ｦ","ﾝ",
    "ｧ","ｨ","ｩ","ｪ","ｫ",
    "ｬ","ｭ","ｮ","ｯ",
    "ｰ"
  ];

  // ▼ オブジェクト形式の変換マップを作成
  // 例: map["ア"] = "ｱ"
  const map = {};
  for (let i = 0; i < zen.length; i++) {
    map[zen[i]] = han[i];
  }

  // ▼ 実際の置換処理
  // 正規表現で見つかった「全角カタカナのかたまり」を
  // コールバックで一文字ずつ半角に変換する
  const result = str.replace(regex, (match) => {
    let out = "";
    for (let ch of match) {
      // マップに存在すれば変換、なければ元の文字をそのまま残す
      out += (map[ch] !== undefined ? map[ch] : ch);
    }
    return out;
  });

  return result;
}

/**
 * テスト用関数
 * Logger.log で結果を確認します。
 */
function testConvert() {
  const s = "アイあウエいオガ漢ギグゲ＆ゴカ！ナ";
  const converted = convertZenKanaToHan(s);
  Logger.log(converted);
  // 期待される出力例: "ｱｲあｳｴいｵｶﾞ漢ｷﾞｸﾞｹﾞ＆ｺﾞｶ！ﾅ"
}

function ZEN2HAN(input) {
  return convertZenKanaToHan(input);
}

=ZEN2HAN(A1)