async open()

in workbox-v4.3.1/workbox-core.dev.js [1043:1083]
32 lines of code
5 McCabe index (conditional complexity)

    async open() {
      if (this._db) return;
      this._db = await new Promise((resolve, reject) => {
        // This flag is flipped to true if the timeout callback runs prior
        // to the request failing or succeeding. Note: we use a timeout instead
        // of an onblocked handler since there are cases where onblocked will
        // never never run. A timeout better handles all possible scenarios:
        // https://github.com/w3c/IndexedDB/issues/223
        let openRequestTimedOut = false;
        setTimeout(() => {
          openRequestTimedOut = true;
          reject(new Error('The open request was blocked and timed out'));
        }, this.OPEN_TIMEOUT);
        const openRequest = indexedDB.open(this._name, this._version);

        openRequest.onerror = () => reject(openRequest.error);

        openRequest.onupgradeneeded = evt => {
          if (openRequestTimedOut) {
            openRequest.transaction.abort();
            evt.target.result.close();
          } else if (this._onupgradeneeded) {
            this._onupgradeneeded(evt);
          }
        };

        openRequest.onsuccess = ({
          target
        }) => {
          const db = target.result;

          if (openRequestTimedOut) {
            db.close();
          } else {
            db.onversionchange = this._onversionchange.bind(this);
            resolve(db);
          }
        };
      });
      return this;
    }