Get the last item given an Array, Set, Map or object.

last-item.js

const lastItem = (list) => {
  if (Array.isArray(list)) {
    return list.slice(-1)[0];
  }

  if (list instanceof Set) {
    return Array.from(list).slice(-1)[0];
  }

  if (list instanceof Map) {
    return Array.from(list.values()).slice(-1)[0];
  }

  if (!Array.isArray(list) && typeof list === "object") {
    return Object.values(list).slice(-1)[0];
  }

  throw Error(`argument "list" must be of type Array, Set, Map or object`);
};

// Usage
const l1 = lastItem(["a", "b", "c"]);
// c

const l2 = lastItem(new Set(["d", "e", "f"]));
// f

const l3 = lastItem(
  new Map([
    ["a", "x"],
    ["b", "y"],
    ["c", "z"]
  ])
);
// z

const l4 = lastItem({ a: "x", b: "y", c: "z" });
// z