_onStateChanged listener is only once?

I wrote the example.
https://pub.dartlang.org/packages/flutter_webview_plugin#-example-tab-

I pushed "Open widget webview" button.
The example show log text `onStateChanged: WebViewState.startLoad` and `onStateChanged: WebViewState.finishLoad` in the bottom.

I pushed "Open widget webview" button again, but it didn't show log text again.
Why only once?

I just want to do is that call JS when WebviewScaffold's url finish.

Start with the linked package example and the WebViewScaffold usage around the onStateChanged logs. Reproduce opening the webview twice, then trace when the state listener emits startLoad and finishLoad. Done means the reported behavior is explained or corrected and the example demonstrates calling JavaScript after the URL finishes loading.

Written by the indexing model from the issue text.