Too Long; Didn't Read
Skypack is a CDN service that transpiles node packages to be able to work well in the browser. Many packages in NodeJS are already shipped with ES Module files. ES Module has the advantage of static analysis, tree shaking, and asynchronous. But some transpilers and workarounds are still required. At the time of this writing, in the top 10 depended packages on NodeJS, only tslib supports ES Module. It's recommended way for React to get started is to include the UMD version in UMD.