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>}`)
this.gfx.beginDrawing({
        transform,
        viewport,
        transparency,
        background,
      });
      this.operatorListIdx = 0;
      this.graphicsReady = true;
      if (this.graphicsReadyCallback) {
        this.graphicsReadyCallback();
      }
    }
    cancel(error = null) {
      this.running = false;
      this.cancelled = true;
      if (this.gfx) {
        this.gfx.endDrawing();
      }
      if (this._canvas) {
        canvasInRendering.delete(this._canvas);
      }
      this.callback(
        error ||
          new RenderingCancelledException(
            `Rendering cancelled, page ${this._pageIndex + 1}`,
            "canvas"
          )
      );
    }
    operatorListChanged() {