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>}`)
return this._readyCapability.promise;
    }
    get port() {
      return this._port;
    }
    get messageHandler() {
      return this._messageHandler;
    }
    _initializeFromPort(port) {
      this._port = port;
      this._messageHandler = new MessageHandler("main", "worker", port);
      this._messageHandler.on("ready", function () {
        
        
      });
      this._readyCapability.resolve();
    }
    _initialize() {