Hi there TigerZhao007,
Welcome to Observable. I hope that you find this platform useful and the community welcoming.
I empathize with the difficulties of encountering links to Observable notebooks via blocks.org examples. I too was surprised to find links to ‘standard’ blocks have started to point to Observable, such as with the Sankey, radial stacked bar, and Diamonds II… among others. I also often wish to use visualizations offline, in locally-hosted papers. As shown by my activity on this forum, I’ve encountered a lot of questions and challenges trying to move between Observable and standard / traditional JS.
As a newcomer to JS in general myself, I would encourage you to stick with Observable for a time. Observable’s helped me to understand how pieces of a script play together… to be able to see more clearly which elements can be separated out, which must stay together, etc. Hopefully you’ll also find that your knowledge of D3 will improve more rapidly by tinkering with it in Observable.
Otherwise, except for Mike’s blocks, few (if any) of the bl.ocks.org examples link to Observable. I agree it would be cool of we could also see the original bl.ocks.org examples where they now link to Observable (and maybe Mike can figure out a way to do this), but barring that, there’s still an expansive world of examples online… so hopefully you don’t feel forced into a learning approach that doesn’t fit you.
Sorry if this isn’t much help. The Observable community has been really caring and helpful toward me. I encourage you to ask questions where you do have difficulties. And again - welcome!