Actually for now these libraries are identical and have feature parity. What is the purpose of having two identical libraries? Because PnPjs is an evolution of original PnP-JS-Core. Consider below points regarding new library:
- new organization name (github/pnp) corresponds to npm modules names (@pnp/)
- new library has better structure organization – there are multiple logically divided modules, thus making support and extensibility easier
- new library has exactly the same API and features as current PnP-JS-Core
- new library is a part of SharePoint Pattern & Practices (SharePoint PnP)
- the same people are behind it – Microsoft and awesome community
- development will be performed simultaneously in two libraries for about 5 months. If one feature is available in PnP-JS-Core, this feature also will be added to PnPjs (and vice versa)
- after 5 months (approximately summer 2018) PnP-JS-Core will be deprecated, it will be available in npm and cdn, however it will never receive new features, because main development will be transitioned to PnPjs (pnp/pnp)
What does it mean for you? If you are starting a new project, use new PnPjs library. If you have a chance to perform an upgrade for your current project, upgrade it to PnPjs. If you have a project with PnP-JS-Core – its fine, because the library will be in npm and on cdn, however new feature won’t be rolled out starting from summer 2018 for PnP-JS-Core specifically.
To listen about upcoming changes checkout PnPjs community call – starting from 19:00. If you want to listen to community calls live – use this calendar invite.
Hope this helps!