I am currently building an Office Add-in for PowerPoint and would like to set the grid spacing using Office JavaScript API. Is this even possible?
I looked through the corresponding API documentation but could not find any hint indicating that setting grid spacing is currently supported.
The Office JavaScript API doesn't provide anything for that. In VBA or COM add-ins you may use the Presentation.GridDistance property which sets or returns a single that represents the distance between gridlines.
You can post or vote for an existing feature request on Tech Community where they are considered when the Office dev team goes through the planning process.