async function testExistsTest2(dbName, storeName, fn)
{
//console.log("dbName:"+dbName+" storeName:"+storeName+" fn:"+fn);
	const db = await databaseOpen(dbName);
	const result = await runTx(db, storeName, "readonly", (store) => 
	{
		return new Promise((resolve, reject) => 
		{
			const req = store.openCursor();
			req.onsuccess = (event) => 
			{
				const cursor = event.target.result;
				if (cursor) 
				{
					if (fn(cursor.value)) 
					{
						resolve(true); // if it is found, it ends immediately.
						return;
					}
					cursor.continue();
				} 
				else 
				{
					resolve(false);//cases where it was not found until the end.
				}
			};
			req.onerror = () => reject(req.error);
		});
	});
	
	db.close();

	return result;
}
function databaseOpen(dbName) 
{
	return new Promise((resolve, reject) => 
	{
		const req = indexedDB.open(dbName);
		req.onsuccess = (event) => 
		{
			resolve(event.target.result);
		};
		req.onerror = () => reject(req.error);
	});
}
function waitForTx(tx) 
{
	return new Promise((resolve, reject) => 
	{
		tx.oncomplete = () => resolve();
		tx.onabort = () => reject(tx.error ?? new Error("Transaction aborted"));
		tx.onerror = () => reject(tx.error);
	});
}

async function runTx(db, storeName, mode, work) 
{
	const tx = db.transaction([storeName], mode);
	const store = tx.objectStore(storeName);
	const result = await work(store);
	await waitForTx(tx);
	return result;
}
testExistsTest2("aaa", "t2", rec => rec.f1 == 1 && rec.f2 >= 1)
.then(result => 
{
	console.log(result);
})
.catch(error => {
	console.error("group by error:", error);
});
//[sample data]
/*
await runTx("aaa", "t2", "readwrite", (store) => 
{
	store.add({ f0: 0, f1: 1, f2: 2, f3: 1, f4: "1,2,1" });
	store.add({ f0: 1, f1: 1, f2: 1, f3: 1, f4: "1,1,1" });
	store.add({ f0: 2, f1: 1, f2: 3, f3: 1, f4: "1,3,1" });
	store.add({ f0: 3, f1: 3, f2: 1, f3: 1, f4: "3,1,1" });
	store.add({ f0: 4, f1: 3, f2: 4, f3: 1, f4: "4,4,1" });
	store.add({ f0: 5, f1: 2, f2: 1, f3: 3, f4: "2,1,3" });
	store.add({ f0: 6, f1: 2, f2: 1, f3: 2, f4: "2,1,2" });
	store.add({ f0: 7, f1: 2, f2: 1, f3: 1, f4: "2,1,1" });
});
*/