There are two issues I met, let me first show my code snippet: 

    Loader {
        id: qtPageLoader
        active: true
        visible: true
        source: "../pages/QtPage.qml"
    }

    function pushQtPage() {
        navPane.push({item: qtPageLoader.item, destroyOnPop: true})
    }

Issue#1, when I enable Projects->Manage Kits... -> Qt Quick -> enable autoformat, when saving files it always padding the push with quotation mark as :     

                    "item": qtPageLoader.item,

                    "destroyOnPop": true

Issue#2, I have to disable aoto format, manually remove quotation mark, then running into error:     

            push: nothing to push

Only this could work:  navPane.push(qtPageLoader.item)

Thanks