Common API - Office.Settings

Represents custom settings for a task pane or content add-in that are stored in the host document as name/value pairs.
The Settings object is saved per add-in and per document.
They are available only to the add-in that created them, and only from the document in which they are saved.

link - learn.microsoft.com/en-us/javascript/api/office/office.settings?view=word-js-preview

addHandlerAsync	M	Adds an event handler for the settingsChanged event.
get	M	Retrieves the specified setting.
refreshAsync	M	Reads all settings persisted in the document and refreshes the content or task pane add-in's copy of those settings held in memory.
remove	M	Removes the specified setting.
removeHandlerAsync	M	Removes an event handler for the settingsChanged event.
saveAsync	M	Persists the in-memory copy of the settings property bag in the document.
set	M	Sets or creates the specified setting.