How to use PostMessage in a React Native webview?

Question

I'm trying to use the postmessage to a page opened in a webview inside a React Native App. I tried many times, but still wasn't able to send it.

I can listen to messages from the webpage normally. I just can't send anything back.

I'm currently using react-native-webview 11.6.5

export default function WebPage() {
  const webviewRef = useRef();

  const onMessage = (event) => {
    //receive message from the web page. working here until here
    const data = JSON.parse(event.nativeEvent.data);

    //reply the message
    webviewRef.current.postMessage(
      JSON.stringify({reply: 'reply'}),
      '*'
    )
  }

  return <View>
    <WebView
      ref={webviewRef}
      originWhitelist={['*']}
      source={{ uri: 'https://robertnyman.com/html5/postMessage/postMessage.html' }}
      domStorageEnabled
      javaScriptEnabled
      onMessage={onMessage}
    />
  </View>


}

Any ideas what am I doing wrong?

UPDATE:

Thanks to @Ahmed Gaber help I was able to find this issue https://github.com/react-native-webview/react-native-webview/issues/809 and discover they're changing postMessage to injectJavaScript.

So I updated my code onMessage to the following:

const onMessage = (event) => {
  const data = JSON.parse(event.nativeEvent.data);

  //reply the message
  webviewRef.current.injectJavaScript(
    `window.postMessage(
      {
        reply: 'reply'
      }
    );`
  )
}

Answer 1

To send data from app to webview, use injectedJavaScript
To send data from webview to app, use postMessage
To receive data in webview sent by postMessage, use onMessage

// This Js function will be injected into the web page after the document finishes loading.
// This function will Post a message to WebView.
const INJECTED_JAVASCRIPT = `(function() {
    window.ReactNativeWebView.postMessage(JSON.stringify({key : "value"}));
})();`;



<WebView
  source={{ uri: 'https://reactnative.dev' }}
  injectedJavaScript={INJECTED_JAVASCRIPT}
  onMessage={(event) => {
       const data = JSON.parse(event.nativeEvent.data);
       alert(data.key);
  }}
/>;