I would have loved something like this while learning to program as well. I mean ... the Ruby REPL was fun, but this sort of thing is just so much more tactile and visual.

We haven't had time to produce as many demo notebooks as we might have liked, but these notebooks really aren't D3-specific in the slightest. They're a reactive flavor of JavaScript, and anything that produces a value or can be rendered to the DOM will work.

For example, here are a whole mess of Plotly charts: https://beta.observablehq.com/@jashkenas/plotly-js

Here are some (wild) WebGL, Three.js and regl sketches: https://beta.observablehq.com/collection/webgl

And here are some simple native inputs you can use to control your sketches: https://beta.observablehq.com/@jashkenas/inputs

Remember — a "slider" here isn't anything special. It's just a chunk of DOM that produces a number as a value. It can be replaced with anything else you can imagine that produces a number as a value. There's no API there ;)