SharePoint Framework
SharePoint Framework (SPFx) is a page and web part model that provides full support for client-side SharePoint development, easy integration with SharePoint data, and support for open source tooling. It enables developers to build responsive, modern web parts and extensions that run in SharePoint Online and SharePoint Server 2016 and later, using JavaScript frameworks like React, Angular, or plain JavaScript/TypeScript.
Developers should learn SPFx when building custom solutions for SharePoint environments, as it is the modern, supported way to create web parts, extensions, and applications that integrate seamlessly with SharePoint. It is essential for extending SharePoint functionality, creating custom user interfaces, and developing business applications that leverage SharePoint data and services, particularly in Office 365 and hybrid deployments.