Fix the greedy pick by insertion order — find the bug

const graph = new Map([["a", [["c", 4], ["b", 1]]], ["b", [["c", 2]]], ["c", []]]);
const dist = new Map([["a", 0]]);
const done = new Set();
for (;;) {
  let best = null;
  for (const [node] of dist) if (!done.has(node)) { best = node; break; }
  if (best === null) break;
  done.add(best);
  for (const [next, w] of graph.get(best) || []) {
    const cand = dist.get(best) + w;
    if (!dist.has(next)) dist.set(next, cand);
  }
}
document.querySelector('#out').textContent = "cost " + dist.get("c");