QJSValue type properties are not supported in QML

Cannot assign values to properties of type QJSValue from QML.

Plugin exposes the property like this:

 class JsonDbCachingListModel : public QObject {
    Q_PROPERTY(QJSValue customData READ customData WRITE setCustomData) 
    QJSValue customData() const; 
    void setCustomData(const QJSValue &newData);
 }

When assigning value in QML like this

    JsonDb.JsonDbCachingListModel {
        customData: customHeadersCallback.toString()
    }
    function customHeadersCallback(item) {
        return { 'Header' : "Sect" };
    }

The following error is displayed in console : "Unable to assign QString to QJSValue"
If the function is passed directly (without .toString()), the error becomes "Unable to assign a function to a property of any type other than var."

Shouldn't we support all types supported by QJSValue (like string & function) ?