Depending on your scenarios and objectives, you can choose from two technologies to access and extend Excel: Office Add-ins and the Microsoft Graph REST API.
Extend Excel functionality with Office Add-ins
With the Office Add-ins platform, you can extend Excel’s functionality through a web app that runs within the Excel client on multiple platforms such as Windows, Online, Mac OS, iPad. This technology is enabled using the JavaScript API for Office known as Office.js. To learn more about creating an Excel add-in with Office.js, see Excel add-ins documentation.
With Microsoft Graph, you can read and modify Excel workbooks that are stored in OneDrive, SharePoint, or other supported storage platforms. By issuing REST API requests to Microsoft Graph, your web or mobile application can access Excel objects. To learn more, see Working with Excel in Microsoft Graph.