 req = window.indexedDB.open(this._databaseName);
				req.onupgradeneeded = (ev) => {
					const db = ev.target.result;
					const oldVersion = ev.oldVersion;
					this._createStores(db, oldVersion);
				}; 
				await reqAsPromise(req);
				this._database = req.result;
			}

			_createStores(db) {
				db.createObjectStore("timeline", {keyPath: ["roomId", "sortKey"]});
			}

			async insert(value) {
				const tx = this._database.transaction(["timeline"], "readwrite");
				const store = tx.objectStore("timeli