https://github.com/mozilla/pdf.js/blob/0df1a5661958df0c4ed2f73b0f3266d825c5c280/src/display/api.js#L710-L719
The return type signature `@returns {Promise<{num: number, gen: number}>}` is mismatched with its definition. (should be `@returns {Promise<number>}`)
});
          const sendTest = () => {
            const testObj = new Uint8Array([
              this.postMessageTransfers ? 255 : 0,
            ]);
            
            
            try {
              messageHandler.send("test", testObj, [testObj.buffer]);
            } catch (ex) {
              warn("Cannot use postMessage transfers.");
              testObj[0] = 0;
              messageHandler.send("test", testObj);
            }
          };
          
          
          
          
          sendTest();
          return;
        } catch (e) {
          info("The worker has been disabled.");
        }
      }
      
      
      this._setupFakeWorker();
    }
    _setupFakeWorker() {