Missing Map Keys

Provide a fallback when a map lookup is missing.

map_default.js

const item = "milk";
const label = new Map([
  ["tea", "drink"],
  ["bread", "food"],
]).get(item) ?? "missing";

console.log("item=" + item);
console.log("label=" + label);

map-default `Map.get` returns `undefined` when the key is missing. The nullish coalescing operator `??` can turn that missing value into a clear fallback label.