webview_flutter javascript channel can't communicate in release mode - reactjs

Question

I am using webview_flutter with version 3.0.0 in my app. I have heavy usage of two-way communication between flutter and javascript. Everything works on debug mode nicely. But, after I build the APK started to get some errors in the javascript channel. I tried with flutter run --release and got the same error.
In my web application (ReactJs), I am using channels in this way:
index.html
<div id="root">
<script>
function sendToFlutter(message) {
if (flutterChannel) {
flutterChannel.postMessage(message);
}
}
</script>
</div>
calling is from React component like this:
window.sendToFlutter("hello-world");
My Webview setup from Flutter end:
Completer<WebViewController> webViewCompleter = Completer<WebViewController>();
WebView(
debuggingEnabled: false,
initialUrl: "https://example.com",
javascriptMode: JavascriptMode.unrestricted,
onWebViewCreated: (WebViewController webViewController) {
webViewCompleter.complete(webViewController);
},
javascriptChannels: <JavascriptChannel>{
JavascriptChannel(
name: "flutterChannel",
onMessageReceived: (JavascriptMessage message) {
if (message.message == "hello-world") {
// Do something
}
})
},
navigationDelegate: (NavigationRequest request) {
if (request.url.startsWith('https://www.youtube.com/')) {
return NavigationDecision.prevent;
}
return NavigationDecision.navigate;
},
gestureNavigationEnabled: true,
zoomEnabled: false,
userAgent: Platform.isAndroid ? kAndroidUserAgent : kIosUserAgent,
);
When I call the channel from ReactJs, then I am getting this error:
TypeError: flutterChannel.postMessage is not a function

Answer 1

According to alexbatalov's research in https://github.com/flutter/flutter/issues/92548, the current workaround is to do the following:
Create android/app/proguard-rules.pro. At minimum you need to have a
rule for JavascriptInterface, but I recommend to copy entire
proguard-android.txt, given the fact that you don’t have these rules.
# Preserve annotated Javascript interface methods.
-keepclassmembers class * {
#android.webkit.JavascriptInterface <methods>;
}