let arr = [1, 2, 3]
arr.push(4, 5)
let res = arr.push(4, 5) //返回值為插入元素后數(shù)組的長(zhǎng)度（res：5）
console.log(arr) // [1, 2, 3, 4, 5]

let arr = [1, 2, 3]
arr.unshift(-2, -1, 0)
let res = arr.unshift(-2, -1, 0) //返回值為插入元素后數(shù)組的長(zhǎng)度（res：6）
console.log(arr) // [-2, -1, 0, 1, 2, 3]

let arr = [1, 2, 3]
arr.pop()
let res = arr.pop() // 返回值為刪除的元素(res: [3])
console.log(arr) // [1, 2]

let arr = [1, 2, 3]
arr.shift()
let res = arr.shift() // 返回值為刪除的元素(res: [1])
console.log(arr) // [2, 3]

// 淺拷貝
let arr = [1, 2, 3]
let newArr = arr.slice() // 返回值為截取后的新數(shù)組
console.log(newArr) // [1, 2, 3] 

//截取元素
let arr = [1, 2, 3]
let newArr = arr.slice(0, 2) // 從第下標(biāo)為0的元素開(kāi)始截取，到元素下標(biāo)為2的元素（注：但不包括元素下標(biāo)為2的元素）
console.log(newArr) // [1, 2]
console.log(arr) // [1, 2, 3] // 不改變?cè)瓟?shù)組

// 新增元素
let arr = [1, 3, 5]
arr.splice(1, 0, 2) // 在元素下標(biāo)為1的元素后面新增一個(gè)元素2
let res = arr.splice(1, 0, 2) // 由于此處為新增元素，返回值為空數(shù)組[]（res： []） 
console.log(arr) // [1, 2, 3, 5]

//刪除元素
let arr = [1, 2, 3]
arr.splice(1, 1) // 在元素下標(biāo)為1的元素后面刪除一個(gè)元素
let res = arr.splice(1, 1) // 返回值為刪除的元素(res: [2])
console.log(arr) // [1, 3]

let arr = ['zbw', 'cyl']
let res = arr.join(',') 
console.log(res) // 'zbw, cyl'

let res = arr.join('-')
console.log(res) // 'zbw-cyl'

let arr1 = [1, 2, 3]
let arr2 = [4, 5, 6]

let res = arr1.concat(arr2)
console.log(res) // [1, 2, 3, 4, 5, 6]

let res = arr1.concat(4, arr2, 7, 8)
console.log(res) // [1, 2, 3, 4, 4, 5, 6, 7, 8]

let arr = [1, 2, 3, 4]
let res = arr.map(item => item * 2)
console.log(res) // [2, 4, 6, 8]

let arr = [1, 2, 3, 4]
let res = arr.filter(item => item >= 2)
console.log(res) // [2, 3, 4]

// 求和
let arr = [1, 2, 3, 4]
let res = arr.reduce((pre, cur) => {
  return pre += cur
}, 0) // 這里是求和 所以初始值為0
console.log(res) // 10

// 數(shù)組轉(zhuǎn)對(duì)象
let arr = [
  { id: 1, name: 'zbw', age: 18 },
  { id: 2, name: 'cyl', age: 18 },
]

let obj = arr.reduce((pre, cur) => {
   pre[cur.id] = cur.name
   return pre
}, {}) // 這里是數(shù)組轉(zhuǎn)對(duì)象 所以初始值為空對(duì)象{}

console.log(obj) // {1: 'zbw', 2: 'cyl'} 

let arr = [
  { name: 'zbw', age: 22 },
  { name: 'cyl', age: 18 },
]

arr.forEach(item => item.age = 20)
console.log(arr) // [{ name: 'zbw', age: 20 },{ name: 'cyl', age:20 }]

let arr = [1, 2, 3, 4]
let bool = arr.some(item => item > 2)
console.log(bool) // true 因?yàn)榇嬖诖笥?的元素

let bool = arr.some(item => item > 5)
console.log(bool) // false 因?yàn)椴淮嬖诖笥?的元素

let arr = [1, 2, 3, 4]
let bool = arr.every(item => item > 0)
console.log(bool) // true 因?yàn)樗性囟即笥?

let bool = arr.every(item => item > 1)
console.log(bool) // false 因?yàn)榇嬖诓淮笥?的元素

let arr = [{ id: 1, name: 'zbw', age: 18 }, { id: 2, name: 'cyl', age: 18 }]

let res = arr.find(item => item.age === 18)
console.log(res) // { id: 1, name: 'zbw', age: 18 }

let res = arr.find(item => item.id === 2)
console.log(res) // { id: 2, name: 'cyl', age: 18 }

let arr = [1, 2, 3];
arr.push(4);        // [1,2,3,4]
arr.pop();          // 4，arr變?yōu)閇1,2,3]
arr.unshift(0);     // [0,1,2,3]
arr.shift();        // 0，arr變?yōu)閇1,2,3]
arr.splice(1, 1, 'a', 'b'); // 從索引1刪除1個(gè)元素，然后插入'a','b' → [1,'a','b',3]

let arr = [1, 2, 3, 2, 1];
arr.indexOf(2);      // 1
arr.lastIndexOf(2);  // 3
arr.includes(3);     // true

// find 示例
let users = [{id:1, name:'A'}, {id:2, name:'B'}];
users.find(u => u.id === 2); // {id:2, name:'B'}
users.findIndex(u => u.name === 'B'); // 1

let arr = [1, 2, 3, 4];
arr.forEach(v => console.log(v * 2));          // 輸出2,4,6,8
let doubled = arr.map(v => v * 2);             // [2,4,6,8]
let evens = arr.filter(v => v % 2 === 0);      // [2,4]
let sum = arr.reduce((acc, cur) => acc + cur, 0); // 10
let hasEven = arr.some(v => v % 2 === 0);      // true
let allPositive = arr.every(v => v > 0);       // true

let arr = [3, 1, 4, 2];
arr.sort();                 // [1,2,3,4] (字符串排序)
arr.sort((a,b) => a - b);   // 升序 [1,2,3,4]
arr.sort((a,b) => b - a);   // 降序 [4,3,2,1]

let nums = [1,2,3];
nums.reverse();             // [3,2,1]

let filled = [1,2,3,4];
filled.fill(0, 1, 3);       // [1,0,0,4]

let arr1 = [1,2];
let arr2 = [3,4];
arr1.concat(arr2);        // [1,2,3,4]

let arr = [1,2,3,4,5];
arr.slice(1, 3);          // [2,3]

let nested = [1, [2, [3, [4]]]];
nested.flat(2);           // [1,2,3,[4]]

let words = ["hello", "world"];
words.flatMap(w => w.split('')); // ['h','e','l','l','o','w','o','r','l','d']

// 復(fù)制自身內(nèi)部片段
let arr = [1,2,3,4,5];
arr.copyWithin(0, 3, 5);  // [4,5,3,4,5]

// 不修改原數(shù)組的方式 (ES2023+)
let original = [3,1,2];
let sortedCopy = original.toSorted();    // [1,2,3]
let reversedCopy = original.toReversed();// [2,1,3]
let replacedCopy = original.with(1, 99); // [3,99,2]
// original 仍然是 [3,1,2]