Call javascript from dart native/flutter

Embed a WebView in your app and use it to run JavaScript:

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

main() {
  runApp(_Test());
}

class _Test extends StatelessWidget {
  final completer = Completer<WebViewController>();

  @override
  Widget build(BuildContext context) {
    var js = '1+1';
    return MaterialApp(
      home: Scaffold(
        body: Stack(
          children: [
            WebView(
              javascriptMode: JavascriptMode.unrestricted,
              onWebViewCreated: (controller) {
                if (!completer.isCompleted) completer.complete(controller);
              },
            ),
            Center(
              child: FutureBuilder(
                future: completer.future.then((controller) {
                  return controller.runJavascriptReturningResult(js);
                }),
                builder: (context, snapshot) {
                  if (snapshot.hasError) throw snapshot.error!;
                  if (!snapshot.hasData) return Container();
                  return Text('$js=${snapshot.data}', style: Theme.of(context).textTheme.headline2);
                },
              ),
            ),
          ],
        ),
      ),
    );
  }
}