index.js

const transaction = db.transaction(["items"], "readwrite");
transaction.oncomplete = function(event) {
  console.log("完了しました");
};
transaction.onerror = function(event) {
  console.log("エラーです", event);
};

const objItem = transaction.objectStore("items");
for (let i = 1; i < 10; i += 1) {
  objItem.add(
    {id: i, name: `テスト商品 ${i}`, description: `テスト商品 ${i} の説明`, add: '追加'}
  ).onsuccess = function (event) {
    console.log(event.target.result);
  }
}