SPFx

The SharePoint Framework (SPFx) is Microsoft's modern client-side development model for building extensions to SharePoint Online, Microsoft Teams, Outlook, and Microsoft 365 Copilot. SPFx solutions are JavaScript / TypeScript / React applications hosted on Microsoft's CDN, packaged as .sppkg files, deployed to the App Catalog and surfaced as web parts, extensions, Teams tabs, or Copilot agent extensions. Replaces the legacy server-side full-trust development model that was eliminated in SharePoint Online. The development stack is Node.js LTS + Yeoman + gulp + TypeScript + React, with PnPjs as the friendly Graph / SharePoint REST wrapper.