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docs: clarify FlutterLoader.loadEntrypoint deprecation #13858

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docs: clarify FlutterLoader.loadEntrypoint deprecation
lamek Sep 4, 2026
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docs: suggest flutter_bootstrap.js for default initialization
lamek Sep 4, 2026
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47 changes: 45 additions & 2 deletions sites/docs/src/content/platform-integration/web/initialization.md
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Original file line number Diff line number Diff line change
Expand Up @@ -260,7 +260,9 @@ _flutter.loader.load({
});
```

## Common warning
## Common warnings {:#common-warnings}

### Service worker version deprecation
Comment on lines +263 to +265

@conooi conooi Sep 4, 2026

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Per the Google dev style guide and Flutter doc guidelines, avoid stacking headings without intervening text!

Suggested change
## Common warnings {:#common-warnings}
### Service worker version deprecation
## Common warnings {:#common-warnings}
This section describes common web build and initialization warnings
and how to resolve them.
### Service worker version deprecation


If you experience a warning similar to the following:

Expand All @@ -269,8 +271,49 @@ Warning: In index.html:37: Local variable for "serviceWorkerVersion" is deprecat
Use "{{flutter_service_worker_version}}" template token instead.
```

You can fix this by deleting the following line from the `web/index.html` file:
Delete the following line from the `web/index.html` file:

```html title="web/index.html"
var serviceWorkerVersion = null;
```

### FlutterLoader.loadEntrypoint deprecation

If you experience a warning similar to the following:

```text
Warning: In index.html:40: "FlutterLoader.loadEntrypoint" is deprecated.
Use "FlutterLoader.load" instead.
```

This warning occurs when an older `web/index.html` file uses
`_flutter.loader.loadEntrypoint()` instead of `_flutter.loader.load()`.
The CLI message references the `FlutterLoader` interface,
which JavaScript code accesses through `_flutter.loader`.

If your app uses the default initialization and doesn't require
custom bootstrapping, replace the legacy script block in `web/index.html`
with the standard script tag:

```html title="web/index.html"
<script src="flutter_bootstrap.js" async></script>
```

If you customized your initialization logic,
update your bootstrap code in `web/index.html`
(or a custom `web/flutter_bootstrap.js` file)
to call `_flutter.loader.load()` instead:

```js
_flutter.loader.load({
onEntrypointLoaded: async function(engineInitializer) {
const appRunner = await engineInitializer.initializeEngine();
await appRunner.runApp();
}
});
```

To review an example that updates DOM elements during startup,
consult the [progress indicator example][].

[progress indicator example]: #example-display-a-progress-indicator
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