QML WebVIew and `runJavaScript()` with WinRT WebView

[daljit97]

So I tried to run the following code on Windows 10 (Qt 5.13):

import QtQuick 2.13
import QtQuick.Window 2.13
import QtQuick.Controls 2.12
import QtWebView 1.1

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    WebView{
        id: webView
        anchors{
            top: button.bottom
            bottom: parent.bottom
            left: parent.left
            right: parent.right
        }

        url: "http://google.com"
    }
    Button{
        id: button
        text: "Click me"
        onClicked: {
            console.debug("Running javascript")
            webView.runJavaScript("document.title", function(result) { console.log(result); });
        }
    }
}

When I click the button I get the following:

qt.winrtrunner.app: The WinRT WebView only supports calling global functions, so please make your call in the form myFunction(a, b, c). Also note that only string arguments can be passed.

What does that mean? Why isn't the console displaying the title of the website? Also could someone clarify for me what is the "callback" function in WebView::runJavascript(script, variant callback)?