[jake-low]

This looks like a great new introduction to D3. It uses Observable as an interactive playground for D3 example code, which I think is an ideal environment for teaching concepts like these. I hope this will help more folks get started in visualization.

If anyone hasn't given Observable a try yet, I highly encourage you to do so. It's more than just "IPython/Jupyter but for JavaScript" — it's reactive, like a spreadsheet. You define "cells" of JS code that are automatically re-evaluated whenever one of their dependencies (another cell) changes.

It's an amazingly productive programming environment. These days, most of my JavaScript projects start off as Observable notebooks because it's such a great platform for experimentation. And I find myself wishing for Observable's features whenever I'm developing in other languages.

I know reactive programming is nothing new, but Observable has been my first opportunity to use it regularly, by "backporting" reactivity into one of the languages I work in most often. Being able to use it for prototyping and visualization for the past couple years has given me a really warm, fuzzy, "what-a-time-to-be-alive" feeling.