Observable is like Jupyter for Javascript. A general JS notebook environment, with the added twist that it uses reactive dataflow ideas to evaluate cells in a "

Observable is like Jupyter for Javascript. A general JS notebook environment, with the added twist that it uses reactive dataflow ideas to evaluate cells in a "right" and deterministic order (a common footgun in Jupyter where cells might be reevaluated manually, resulting in unexpected state). D3 is a JS library for data visualisations. Both are the brainchild of Mike Bostock. That's the connection. :)