how to read response when user click button in webview flutter

i have flutter code using webview and use webview_flutter package, inside my webview i use url from typeform.com how can i get a response when the user clicks the submit button in the webview

Widget _webViewReader = WebView(
       initialUrl: _viewModel.destinationUrl,
       javascriptMode: JavascriptMode.unrestricted,
       javascriptChannels: {
         JavascriptChannel(
           name: JS_CHANNEL_NAME,
           onMessageReceived: jsChannelHandler,
         ),
       },
       onWebViewCreated: (WebViewController controller) {
         _controller.complete(controller);
       },
       onPageFinished: (url) => onPageFinished(url),
     );