Flutter web-hosted app doesn't recognize external functions


I’m hosting a web made on Flutter on GitHub pages and I’m using Dart-JS interop for connecting a Solana wallet. When I test locally I can connect to it and works fine but once I host the web on GitHub Pages I get the following error: Uncaught TypeError: p.isPhantomInstalled is not a function

This is my Dart code:

    class ClientWallet {
      external Future<void> connect();
      external void disconnect();
      external String get address;
      external Future<void> signTransaction();
      external bool isPhantomInstalled();
    class WalletController extends GetxController {
      Future<void> connectWallet(context) async {
        ClientWallet wallet = ClientWallet();
        if (wallet.isPhantomInstalled()) {
          await promiseToFuture(wallet.connect());
          createSnackbar('success', 'Wallet Connected');
        } else {
          createSnackbar('error', 'No Phantom wallet detected');

This is my JS code:

class ClientWallet {

    constructor() {
        this.address = '';

    async connect() {
        const resp = await window.solana.connect();
        this.address = resp.publicKey.toString();

    address() {
        return this.address;

    isPhantomInstalled() {
        return window.solana && window.solana.isPhantom;

    disconnect() {

var walletModule = { ClientWallet: ClientWallet };

It seems that when hosted, the app doesn’t recognize the external functions? I have no clue why or how to solve it.


After reading your original post on connecting a Phantom wallet with Flutter, I decided to try it out myself, and I eventually ran into the same issue as you, down the to exact function call!

The solution (workaround) for me was to use standalone functions instead of methods.

I do not know why, but for some reason the Dart-JS interop stopped working on class instances after flutter build web. My minified JS code with class instances played nice with flutter run -d chrome.


This is the phantom.ts I got working.

const solanaWeb3 = require('@solana/web3.js');

export async function connect(): solanaWeb3.PublicKey {
  const resp = await window.solana.connect();
  return new solanaWeb3.PublicKey(resp.publicKey.toString());

export function disconnect() {

export function isPhantomInstalled(): bool {
  return window.solana && window.solana.isPhantom;

export async function signTransaction(tx: solanaWeb3.Transaction): solanaWeb3.Transaction {
  return await window.solana.signTransaction(tx);

Then Dart-side, the interop is the same, just no class definition. I’m going to write a Medium post / release a GitHub repo with an example soon.

Edit 2:
Medium post / repo can be found here

Answered By – HelmetFace

Answer Checked By – Terry (FlutterFixes Volunteer)

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