B4J Question B4J JavaFX Webview: JavaScript does not work

Sub B4XPage_Appear
    WebView1.LoadHtml("<h1>Just text, wait</h1>")
    Sleep(3000)
    B4JWebViewSettings(WebView1, "setJavaScriptEnabled", True)
    Me.as(JavaObject).RunMethod("setAlertHandler", Array(WebView1))
    Me.as(JavaObject).RunMethod("setConfHandler", Array(WebView1, "Sure ?"))
    WebView1.LoadHtml("<script> alert('Hello B4J WebView!') </script>")
    Sleep(3000)
    WebView1.LoadHtml("<script> confirm('Hello B4J WebView ?') </script>")
End Sub


Sub B4JWebViewSettings(wv1 As WebView, parameter As String, value As Boolean)
    wv1.As(JavaObject).RunMethodJO("getEngine", Null).RunMethod(parameter, Array(value))     'Webview1.As(JavaObject).RunMethodJO("getEngine", Null).RunMethod("executeScript", Array(js))
End Sub

Sub jsAlert(s As String)'ignore
    xui.MsgboxAsync(s, "Information:")
End Sub


#if java
import javafx.scene.web.*;
import javafx.event.*;
import javafx.util.Callback;
import javafx.scene.web.WebView;
import javafx.scene.web.WebEngine;
import javafx.scene.control.Alert;
import javafx.scene.control.Alert.AlertType;
import java.util.Optional;
import javafx.scene.control.ButtonType;

public void setAlertHandler(WebView wv) {

 wv.getEngine().setOnAlert(new EventHandler<WebEvent<String>>(){

            @Override
            public void handle(WebEvent<String> arg0) {           
               callerAlert(arg0.getData());
            }
        });
}
public void callerAlert(String s){
    try{
    _jsalert(null, s);    // lazy way to call sub
    } catch (Exception e) {
    }
}
// set the handler
public static void setConfHandler(WebView wv, String msg){
    WebEngine we = wv.getEngine();
    we.setConfirmHandler(new Callback<String, Boolean>() {
       @Override public Boolean call(String msg) {
          Boolean confirmed = confirm(msg);
          return confirmed;
           }
      });
}
//show the dialog box
private static boolean confirm(String msg){
    Alert alert = new Alert(AlertType.CONFIRMATION);
    alert.setTitle("Are you sure ?");
    alert.setHeaderText(msg);

    Optional<ButtonType> result = alert.showAndWait();
    if (result.get() == ButtonType.OK){
       return true;
    } else {
       return false;
    }
}
#End If