Treffer: Exploring the JavaScript API for Office: Mail Apps.

In this article, the author provides an in-depth look at the JavaScript application programming interface (API). She discusses the fundamental features of the JavaScript API for Office which includes controlling activation based on item type, item access and entries, and well-known entities. She tells that a mail application (app) can use the JavaScript API for Office and EWS callback tokens to access attachments of the currently selected message or appointment in the user's mailbox.