Local & Session Storage in flutter web

import 'package:flutter/material.dart';

class SignupPage extends StatefulWidget {
  SignupPage({
    Key key,
  }) : super(key: key);

  @override
  _SignupPageState createState() => _SignupPageState();
}

class _SignupPageState extends State<SignupPage> {
  String localStorage;
  String sessionStorage;
  GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();
  @override
  Widget build(BuildContext context) {
    // read preference
    TextEditingController controller = TextEditingController();
    localStorage = window.localStorage['local_value'] ?? "No Value Saved";
    sessionStorage =
        window.sessionStorage['session_value'] ?? "No Value Stored";
    return Scaffold(
      key: scaffoldKey,
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TextField(
              controller: controller,
              decoration: InputDecoration(
                  hintText: "Enter value to store as local & session storage",
                  border: OutlineInputBorder()),
            ),
            RaisedButton(
              child: Text("Submit"),
              onPressed: () {
                setState(() {
                  if (controller.text.isNotEmpty) {
                    print(controller.text);
                    window.localStorage['local_value'] = controller.text;
                    window.sessionStorage['session_value'] =
                        controller.text;
                  } else {
                    scaffoldKey.currentState.showSnackBar(SnackBar(
                      backgroundColor: Colors.red,
                      content:
                          Text("Please enter a value before submitting..."),
                    ));
                  }
                });
              },
            ),
            Text("From Local Storage: " + localStorage),
            Text("From Session Storage: " + sessionStorage ?? "No value"),
          ],
        ),
      ),
    );
  }
}