Main.java

package sample;

import javafx.application.Application;
import javafx.application.Platform;
import javafx.scene.Scene;
import javafx.scene.control.SplitPane;
import javafx.scene.control.TextArea;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;
import javafx.stage.Stage;
import rx.subjects.BehaviorSubject;

import static java.util.concurrent.TimeUnit.*;

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) throws Exception{
        TextArea textArea = new TextArea();
        WebView webView = new WebView();
        WebEngine engine = webView.getEngine();

        BehaviorSubject<String> textSubject = BehaviorSubject.create( "" ) ;
        textArea.textProperty().addListener( ( control, oldValue, newValue ) -> textSubject.onNext( newValue ) ) ;
        textSubject.sample( 500, MILLISECONDS )
                   .distinctUntilChanged()
                   .subscribe( ( s ) -> Platform.runLater( () -> engine.loadContent( s ) ) ) ;
        SplitPane root = new SplitPane();
        root.getItems().addAll(textArea, webView);
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }


    public static void main(String[] args) {
        launch(args);
    }
}

I have written a short blogpost about this topic: http://www.guigarage.com/2014/03/reactive-programming-javafx/