Maps and Sets

Map Lookup

Read a value by key from a Map.

map-lookup A `Map` stores key-value pairs. Use `.get(key)` when the lookup key is data instead of a fixed property name.

Map Lookup

item
map_lookup.js
Replay: real traced execution (multi-file project)
const item = "tea";
const price = new Map([
  ["tea", 3],
  ["cake", 5],
  ["juice", 4],
]).get(item);

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

const item = "cake";
const price = new Map([
  ["tea", 3],
  ["cake", 5],
  ["juice", 4],
]).get(item);

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

const item = "juice";
const price = new Map([
  ["tea", 3],
  ["cake", 5],
  ["juice", 4],
]).get(item);

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

  1. item ← tea, price ← 3

    1const item→ tea = "tea"; //@item="cake", "juice"2const price→ 3 = new Map([3  ["tea", 3],4  ["cake", 5],5  ["juice", 4],6]).get(itemtea);78console.log("item=" + itemtea);9console.log("price=" + price3);
    outputitem=tea
price=3

  1. item ← cake, price ← 5

    1const item→ cake = "cake";2const price→ 5 = new Map([3  ["tea", 3],4  ["cake", 5],5  ["juice", 4],6]).get(itemcake);78console.log("item=" + itemcake);9console.log("price=" + price5);
    outputitem=cake
price=5

  1. item ← juice, price ← 4

    1const item→ juice = "juice";2const price→ 4 = new Map([3  ["tea", 3],4  ["cake", 5],5  ["juice", 4],6]).get(itemjuice);78console.log("item=" + itemjuice);9console.log("price=" + price4);
    outputitem=juice
price=4