node 数组常用方法

//length 可变
var arr = []
arr.length = 10
arr[1] = 2
console.log(arr)
arr.length = 8
console.log(arr)


//index 可以超过length

arr[12] = "f"
console.log(arr)

//push/pop 从尾部读取

arr = [1, 2, 3, 4, 5, 6]
arr.push(12)
console.log(arr)

let a = arr.pop()

console.log(a, arr)

arr.push(...["a", "b", "c"])
console.log(arr)

//shift /unshift 从顶部移除添加
arr.shift()
console.log(arr)

arr.unshift("1", ...[10, "l"])
console.log(arr)

//splice 截取并插入
let arrnew = arr.splice(0, 3, "new", "new1")
console.log(arrnew, "\\n", arr)

//reverse 逆序
arr.reverse()
console.log(arr)

//sort 排序
arr.splice(0, 3)
arr.sort()
console.log(arr)

//new
//arr=new Array()

//Object.values Object.keys Object.entries   取值 取key 数据[[key,value]]
console.log(Object.values(arr))
console.log(Object.keys(arr))
console.log(Object.entries(arr))

let str = "1,2,34,56,,"
arr = str.split(",")
console.log(arr)

//concat   数组连接 返回连接后的数组
arr = arr.concat("new", ...["a", "b", 'c'])
console.log(arr)

//slice

arr1 = arr.slice(1, 3)
console.log(arr1)

//map 类似于foreach
arr.map((v, k, e) => console.log(v))
//求平方
temp = [1, 2, 3]
temp = temp.map(v => v * v)
console.log(temp)

arr.map((v, k) => console.log(`${k}==${v}`))

//filter  筛选
console.log(arr)
arr = arr.filter((v, k) => v > 1)
// arr.filter((v, k) => v > 1).forEach((v, k, s) => {
//     console.log(s)
// })
console.log(arr)

//every 是否所有满足条件
console.log("is null:", arr.every(v => !v))

//some  是否有一个满足
console.log("have >1:", arr.some(v => v > 1))

// includes 包含
console.log("hava 2:", arr.includes('2'))

//foreach  与map 区别 map 会返回新数组
console.log(arr)
arr.forEach(v => v * v)
console.log(arr)

//reduce 累加器 
arr = arr.map(v => parseInt(v))
let total = arr.reduce((base, num) => base + num, 3)
console.log(total)

// arr = ["apple", "orange", "apple", "orange", "pear", "orange"];

// function getWordCnt() {
//     return arr.reduce(function (prev, next) {
//         prev[next] = (prev[next] + 1) || 1;
//         return prev;
//     }, {});
// }

// console.log(getWordCnt());

//find 
let t = arr.find(v => v = 2)
console.log(t)

let index = arr.indexOf(34)
console.log(index)

str = arr.join(',')
console.log(str)