// declare the extended NativeScriptActivity functionality

var extendsObject = {

    onCreate: function(savedState){

        // call the base NativeScriptActivity.onCreate method

        // the "this" variable points to a NativeScriptActivity instance

        this.super.onCreate(savedState);

        // create a button and set it as the main content

        var button = new android.widget.Button(this);

        button.setText("Hello World");

        this.setContentView(button);

    }

}

// pass the extends object to create a new NativeScriptActivity instance

var mainActivity = com.tns.NativeScriptActivity.extends(extendsObject);

var applicationInitObject = {

    getActivity: function(intent) {

        // this method is called whenever a new instance of NativeScriptActivity is about to be created

        return mainActivity;

    },

    onCreate: function() {

        // This is the first method called. Called from the android.app.Application.onCreate method.

    }

}

// The NativeScriptRuntime exposes the app object within the global context

app.init(applicationInitObject);

<Page xmlns="http://www.nativescript.org/tns.xsd" loaded="pageLoaded">

  <StackLayout>

    <Label text="Tap the button" cssClass="title"/>

    <Button text="TAP" tap="{{ tapAction }}" />

    <Label text="{{ message }}" cssClass="message" textWrap="true"/>

    <Button text="test button"/>

  </StackLayout>

</Page>