Office.addin exists for now in Excel and Powerpoint JS addins.
It would definitely be interesting to port this functionality to Outlook JS addin as well.
Office.addin is loaded in Outlook JS addin, so that the taskpane can be shown or hidden.
Right now, Office.addin namespace is not loaded in Outlook JS addin, leaving no choice but to inform the client of the result of a command via Office.context.mailbox.item.notificationMessages.replaceAsync which is not visible enough.
The goal is to be able to open the taskpane from Typescript code while I am executing a command launched from the ribbon.
For instance, I want to show the taskpane while refreshing data, so I can show the process ongoing to the user in a dialog inside the taskpane.
This, whatever the platform is.