Install dev server packages

docker run --rm -w /app -v $PWD:/app -u $(id -u):$(id -u) node bash -c "npm install"

Start the dev server

docker run --rm --init -it -w /app -v $PWD:/app -p 8080:8080 node bash -c "node dev-server.js"

Visit localhost:8080 to view.

Rough way to save the SVG map generated by JavaScript client-side

const XMLS = new XMLSerializer();
const svg_xmls = XMLS.serializeToString(svg);
let bl = new Blob([svg_xmls], {type: "text/html" });
let a = document.createElement("a");
a.href = URL.createObjectURL(bl);
a.download = "map.svg";
a.hidden = true;
document.body.appendChild(a);
a.innerHTML = "something random - nobody will see this, it doesn't matter what you put here";
a.click()