I am working with a partner that wants to avoid having to create a Web Application for their Excel/Word/PowerPoint/OneNote project. They would like everything to remain client side with AJAX calls.
Is there a way to use Graph API from an add-in without having to setup web app scaffolding? For example, in Outlook you have the makeEwsRequestAsync() call to reach back to Exchange and you can do this client side. Is there some similar means to makeGraphRequestAsync()?
I don't know what you mean by "web app scaffolding". Single sign-on capability from web add-ins allows you to access Microsoft Graph without the need for repeated sign-on prompts. However, SSO feature only supported for apps that have a backend application server (Single Page Apps can't use this technology). You can of course make direct web service API calls to Microsoft Graph anytime. The add-in regardless has to be hosted and distributed to users using centralized catalog or through Microsoft Store.
