Why won't my Flutter web app debug open in the browser?

Question

In VScode, I used to be able to go 'Run' -> 'Run without debugging' and if the 'Web server (web-javascript)' was chosen then the Flutter app would open in debug mode in Chrome. This used to open a new Chrome window for the app to be displayed in. I'm not sure what I've done but this no longer works. I now get the message below showing in the debug console. I have tried to go to the localhost link in Chrome but I just get a blank screen and no errors in the Chrome console. I've tried downloading the Dart extension in Chrome but this doesn't help.

Launching lib\main.dart on Web Server in debug mode...
Waiting for connection from Dart debug extension at http://localhost:51367

So far I have tried reinstalling VScode and Flutter, reinstalling the Dart and Flutter extensions. I've even tried to uninstall VScode and remove all the extension and settings files that get left behind (like mentioned here). I've set Flutter up as the Flutter website says every time but none of this has helped and I have no idea what has gone wrong. Could anyone help?

In case it helps, here is the Flutter doctor output:

Downloading android-arm-profile/windows-x64 tools...                1.7s
Downloading android-arm-release/windows-x64 tools...                0.8s
Downloading android-arm64-profile/windows-x64 tools...              1.2s
Downloading android-arm64-release/windows-x64 tools...              1.3s
Downloading android-x64-profile/windows-x64 tools...                2.2s
Downloading android-x64-release/windows-x64 tools...                1.0s
Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel beta, 1.20.0-7.3.pre, on Microsoft Windows [Version 10.0.18362.959], locale en-GB)

[√] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
[√] Chrome - develop for the web
[√] Android Studio (version 4.0)
[√] VS Code (version 1.47.3)
[√] Connected device (2 available)

• No issues found!

Try upgrading Flutter and if not try copying the code to a new project (last resort) — Eind997, Mar 07 '21 at 09:23
# Firebase Error # For me this helped https://stackoverflow.com/questions/64917744/cannot-run-with-sound-null-safety-because-dependencies-dont-support-null-safety — Waqar, Sep 23 '21 at 20:15

Abdelrahman Sherif · Answer 1 · 2022-02-02T10:53:06.490

The problem for me was in the index.html file located in the "web" folder.

The cause for the error was my <script src="main.dart.js" type="application/javascript"></script> line. It was not at the very bottom of the body tag. Moving it to the bottom fixed the issue.

You might also need to re-check the index.html file in general. The general order inside the body tag should be as follows:

1-

 <script>
    if ('serviceWorker' in navigator) {
      window.addEventListener('flutter-first-frame', function () {
        navigator.serviceWorker.register('flutter_service_worker.js');
      });
    }
  </script>

2- (applies to firebase users) Firebase CDN scripts. ex:

<script src="https://www.gstatic.com/firebasejs/7.20.0/firebase-app.js"></script>

3- (Firebase users)

<script>
  // Your web app's Firebase configuration
  var firebaseConfig = {
    apiKey: "<your api key>",
    authDomain: "<your auth domain>",
    projectId: "<Your project id>",
    messagingSenderId: "<your messaging sender id>",
    appId: "<your app id>"
  };
  // Initialize Firebase
  firebase.initializeApp(firebaseConfig);
</script>

4- (most importantly) Make sure this line is at the bottom of the body tag

<script src="main.dart.js" type="application/javascript"></script>

What about code I add for the splash screen? Where in body should it be located? — Rony Tesler, May 28 '21 at 17:00
Hi Rony, I have not implemented a splash screen for web before. I believe this can be easily solved using trial and error? — Abdelrahman Sherif, May 28 '21 at 19:23
I referred to this answer https://stackoverflow.com/a/60019802/9646191 — Abdelrahman Sherif, May 28 '21 at 19:23

orgreeno · Answer 2 · 2020-08-26T15:19:11.333

5

I had to rerun flutter config --enable-web after an upgrade to get it working again. Then restart vscode and run.

edited Aug 26 '20 at 15:19

answered Aug 26 '20 at 14:27

orgreeno

143
2
9

score 3 · Answer 3 · answered Nov 24 '21 at 10:59

if you want to run your flutter web code in a specific port or..., you will see this error.

The web-server device requires the Dart Debug Chrome extension for debugging. Consider using the Chrome or Edge devices for an improved development workflow.
Please click the Dart Debug extension button in the spawned browser window

you can easily install dart extension from dart-extention and click on it every time you run your code.

score 2 · Answer 4 · answered Aug 05 '21 at 16:22

2

For me. All I had to do was to make sure that Chrome was the default browser.

answered Aug 05 '21 at 16:22

surge10

622
6
18

score 1 · Accepted Answer · answered Jul 29 '20 at 12:14

1

Last resort (maybe someone has a better solution). Make a new project and copy the lib across. Add anything needed in the pubspec.yaml

answered Jul 29 '20 at 12:14

Eind997

319
1
3
9

If create new project work, maybe `flutter clean` work as well – Philip Purwoko Jun 17 '21 at 15:56

score 1 · Answer 6 · answered Feb 03 '22 at 07:30

1

Simply open a new tab with the flutter app URL.

answered Feb 03 '22 at 07:30

Edie Kamau

230
1
5

Even opening in incognitodid not work – Krishna Dec 22 '22 at 11:26

score 1 · Answer 7 · answered Apr 26 '22 at 04:52

1

For me, I used an old project that has Android build files. I did the following

flutter config --enable-web
flutter clean
restarting vscode

It solved the problem.

answered Apr 26 '22 at 04:52

Rajesh

3,562
7
24
43

score 1 · Answer 8 · answered May 15 '22 at 14:52

1

I solved it after upgrading flutter to 3.0v.

flutter upgrade

answered May 15 '22 at 14:52

zeev grim

137
1
5

score 1 · Answer 9 · answered Nov 26 '22 at 19:13

Just in case anyone has facing this issue in vscode devcontainer, I had a hard time trying to figure out what was happening, I tried everything, flutter clean, forwarding port in devcontainer. It just happened that the version of flutter that i was using had the issue. I was using 3.6 and change to 3.9, everything is working right now.

score 0 · Answer 10 · answered Dec 22 '22 at 14:33

I was getting a white blank screen and debug console said this

Running "flutter pub get" in flutter_application_1...
Launching lib/main.dart on Web Server in debug mode...
lib/main.dart:1
Waiting for connection from Dart debug extension at http://localhost:42207
The web-server device requires the Dart Debug Chrome extension for debugging. Consider using the Chrome or Edge devices for an improved development workflow.
Please click the Dart Debug extension button in the spawned browser window

flutter run -d web-server in cmd line worked for me though I have to press 'r' manually to reload

score 0 · Answer 11 · answered Feb 14 '23 at 12:14

0

If running on the web check the web console. I had a js function that double declared "index".

answered Feb 14 '23 at 12:14

Brandon Pillay

986
1
12
28

score 0 · Answer 12 · answered Jul 03 '23 at 14:49

0

What worked for me was:

I upgraded Google Chrome on my Ubuntu to the newest version (google the newest version for your OS)
Restarted VsCode

answered Jul 03 '23 at 14:49

Giuseppe Brandi

1
1

Why won't my Flutter web app debug open in the browser?

12 Answers12