`fetch` always returns status 200 even when actual status should be different

[nohackjustnoobb]

When using the fetch API with flutter_js, the returned response object always reports a 200 status code, even if the actual HTTP status code is different. For example, when making a request to https://httpbin.org/status/400, the status is expected to be 400, but the reported resp.status is 200.

Sample Code to Reproduce:

import 'package:flutter/material.dart';
import 'package:flutter_js/extensions/fetch.dart';
import 'package:flutter_js/extensions/xhr.dart';
import 'package:flutter_js/flutter_js.dart';

void main() {
  runApp(const MainApp());
}

class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: FilledButton(
            onPressed: () async {
              final runtime = await getJavascriptRuntime().enableFetch();
              runtime.enableHandlePromises();
              runtime.enableXhr();

              JsEvalResult result = await runtime.evaluateAsync("""
              async function main() {
                console.log("Hello, World!!!");

                const resp = await fetch("https://httpbin.org/status/400");

                console.log("Response status:", resp.status);
              }

              main();
              """);
              runtime.executePendingJob();

              print(result);

              if (result.isPromise ||
                  result.stringResult == "Instance of 'Future<dynamic>'") {
                result = await runtime.handlePromise(result);
              }

              print(result);
            },
            child: Text('Click Me'),
          ),
        ),
      ),
    );
  }
}

Output:

I/flutter ( 2843): Hello, World!!!
I/flutter ( 2843): Instance of 'Future<dynamic>'
I/flutter ( 2843): Response status: 200
I/flutter ( 2843): null

Environment:

• flutter_js version: 0.8.4
• Platform: tested on Android and iOS
• Flutter version: 3.32.0