I'm new at d3. I can't render a US map, could you have a look?
https://codepen.io/DeanWinchester88/pen/BaZYewv
d3.json(COUNTIES)
.then( data => {
let states = topojson.feature(data, data.objects.states);
TopoJSON was never part of any D3 bundle. Therefore, you have to reference it, like:
<script src="https://unpkg.com/topojson@3"></script>
In the CodePen, "Add Package" will create:
import * as topojson from "https://cdn.skypack.dev/topojson@3.0.2";
(and now you'll have brand new errors...)