const users = [
  { id: 1, name: 'Alice', active: true },
  { id: 2, name: 'Bob', active: false },
  { id: 3, name: 'Charlie', active: true },
  { id: 4, name: 'David', active: true }
];

// 找出所有活躍用戶
const activeUsers = users.filter(user => user.active);
console.log(activeUsers);
// 輸出: [
//   {id: 1, name: 'Alice', active: true},
//   {id: 3, name: 'Charlie', active: true},
//   {id: 4, name: 'David', active: true}
// ]

// 沒有匹配項(xiàng)時(shí)
const noUsers = users.filter(user => user.age > 100);
console.log(noUsers); // 輸出: []

// 查找第一個(gè)活躍用戶
const firstActive = users.find(user => user.active);
console.log(firstActive);
// 輸出: {id: 1, name: 'Alice', active: true}

// 沒有匹配項(xiàng)時(shí)
const notFound = users.find(user => user.age > 100);
console.log(notFound); // 輸出: undefined

// 性能測(cè)試
const bigArray = Array(1000000).fill(0).map((_, i) => i);

console.time('filter');
bigArray.filter(x => x === 500000); // 會(huì)檢查所有元素
console.timeEnd('filter'); // 輸出: filter: 5.22509765625 ms

console.time('find');
bigArray.find(x => x === 500000); // 找到后立即停止
console.timeEnd('find'); // 輸出: find: 2.56298828125 ms

// filter可以繼續(xù)鏈?zhǔn)秸{(diào)用
users
  .filter(user => user.active)
  .map(user => user.name)
  .forEach(name => console.log(name));
// 輸出: 
// Alice
// Charlie
// David

// find不能鏈?zhǔn)秸{(diào)用數(shù)組方法（因?yàn)榉祷氐氖窃兀?
const userName = users.find(user => user.id === 2).name; // 直接訪問屬性
console.log(userName) //輸出: Bob

// 獲取所有未完成的任務(wù)
const incompleteTasks = tasks.filter(task => !task.completed);

// 結(jié)合map使用
const activeUserNames = users
  .filter(user => user.active)
  .map(user => user.name);

// 查找特定用戶
const user = users.find(user => user.id === 3);
console.log(user) //輸出: { id: 3, name: 'Charlie', active: true },

// 檢查是否存在管理員
const hasAdmin = users.find(user => user.role === 'admin') !== undefined;
console.log(hasAdmin ) //輸出: false

const found = users.find(u => u.id === 1);
found.name = 'Alex'; // 會(huì)修改原數(shù)組中的對(duì)象
console.log(users) 
//輸出: [
//  { id: 1, name: 'Alex', active: true },
//  { id: 2, name: 'Bob', active: false },
//  { id: 3, name: 'Charlie', active: true },
//  { id: 4, name: 'David', active: true }
// ]

const sparse = [1, , 3];
sparse.find(x => true); // 1 (跳過空位)
sparse.filter(x => true); // [1, 3] (跳過空位)

const checker = {
  threshold: 2,
  check(num) { return num > this.threshold; }
};

[1, 2, 3].find(checker.check, checker); // 3