# PDFViewer.activePanel

```ts
get activePanel(): SidebarTab | null
```

The open sidebar panel, or `null` when the sidebar is collapsed. The [panelChanged](https://kernstra.com/docs/web-sdk/api/events#ev-panelchanged) event reports every change of it.

- Kind: getter
- Since: 1.0.0

Returns `SidebarTab | null`

Part of [PDFViewer](https://kernstra.com/docs/web-sdk/api/pdfviewer) in the Kernstra Web SDK 1.0.0 API reference.

Web page: https://kernstra.com/docs/web-sdk/api/pdfviewer/activepanel