// 創(chuàng)建一個(gè)空 Map
const map = new Map();

// 通過二維數(shù)組初始化 Map
const map2 = new Map([
  ['key1', 'value1'],
  ['key2', 'value2']
]);

const map = new Map([
  ['name', 'Alice'],
  ['age', 25],
  ['job', 'Developer']
]);

// 1. for...of 遍歷
for (const [key, value] of map) {
  console.log(key, value);
}

// 2. forEach 方法
map.forEach((value, key) => {
  console.log(key, value);
});

// 3. 獲取鍵、值或鍵值對(duì)的迭代器
console.log([...map.keys()]);    // ['name', 'age', 'job']
console.log([...map.values()]);  // ['Alice', 25, 'Developer']
console.log([...map.entries()]); // 同直接遍歷 map

function countChars(str) {
  const map = new Map();
  for (const char of str) {
    map.set(char, (map.get(char) || 0) + 1);
  }
  return map;
}

const result = countChars('hello');
console.log(result.get('l')); // 2

const cache = new Map();

function factorial(n) {
  if (cache.has(n)) return cache.get(n);
  if (n === 0) return 1;
  const result = n * factorial(n - 1);
  cache.set(n, result);
  return result;
}

console.log(factorial(5)); // 120
console.log(cache); // Map { 1 => 1, 2 => 2, 3 => 6, 4 => 24, 5 => 120 }

const user1 = { id: 1, name: 'Alice' };
const user2 = { id: 2, name: 'Bob' };

const userSettings = new Map();
userSettings.set(user1, { theme: 'dark' });
userSettings.set(user2, { theme: 'light' });

console.log(userSettings.get(user1)); // { theme: 'dark' }