Error: Property or method "filetypeIcon" is not defined

When adding or editing attachments in devices and platforms, there is an error in the console:

[Vue warn]: Property or method "filetypeIcon" is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property. See: https://vuejs.org/v2/guide/reactivity.html#Declaring-Reactive-Properties.

In fact, the method is not defined in the new and edit pages of the attachments. But there is such a method in components/AttachmentListItem.vue. This should be put into an external file and required in the places where needed.