var arr = [1,2,3,4,5]
for(var i=0;i<arr.length;i++){
  console.log(arr[i])
}

var arr = [1,2,3,4,5]
for(var i=0,len=arr.length;i<len;i++){
  console.log(arr[i])
}

var arr5 = [10,20,30]
var result5 = arr5.forEach((item,index,arr)=>{
    console.log(item)
})
console.log(result5)
/*
10
20
30
undefined   該方法沒有返回值
*/

const nodes = document.querySelectorAll('div')
Array.prototype.forEach.call(nodes,(item,index,arr)=>{
  console.log(item)
})

var arr = [1,2,3,4,5]
for(var i in arr){
  console.log(i,arr[i])
}  //這里的i是對(duì)象屬性，也就是數(shù)組的下標(biāo)
/**
0 1
1 2
2 3
3 4
4 5 **/

let arr=["前端","南玖","ssss"];
    for (let item of arr){
        console.log(item)
    }
//前端 南玖 ssss

//遍歷對(duì)象
let person={name:"南玖",age:18,city:"上海"}
for (let item of person){
  console.log(item)
}
// 我們發(fā)現(xiàn)它是不可以的 我們可以搭配Object.keys使用
for(let item of Object.keys(person)){
    console.log(person[item])
}
// 南玖 18 上海

let arr=[1,2,3];
const res = arr.map(item=>{
  return item+1
})
console.log(res) //[2,3,4]
console.log(arr) // [1,2,3]

var arr = [10,30,25,64,18,3,9]
var result = arr.every((item,index,arr)=>{
      return item>3
})
console.log(result)  //false

var arr2 = [10,20,32,45,36,94,75]
var result2 = arr2.some((item,index,arr)=>{
    return item<10
})
console.log(result2)  //false

const array = [1,2,3,4]
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));

// filter  返回滿足要求的數(shù)組項(xiàng)組成的新數(shù)組
var arr3 = [3,6,7,12,20,64,35]
var result3 = arr3.filter((item,index,arr)=>{
    return item > 3
})
console.log(result3)  //[6,7,12,20,64,35]

//測(cè)試函數(shù)
function clecTime(fn,fnName){
        const start = new Date().getTime()
        if(fn) fn()
        const end = new Date().getTime()
        console.log(`${fnName}執(zhí)行耗時(shí):${end-start}ms`)
}

function forfn(){
  let a = []
  for(var i=0;i<arr.length;i++){
    // console.log(i)
    a.push(arr[i])
  }
}
clecTime(forfn, 'for')   //for執(zhí)行耗時(shí):106ms

function forlenfn(){
  let a = []
  for(var i=0,len=arr.length;i<len;i++){
    a.push(arr[i])
  }
}
clecTime(forlenfn, 'for len')   //for len執(zhí)行耗時(shí):95ms

function forEachfn(){
  let a = []
  arr.forEach(item=>{
    a.push[item]
  })
}
clecTime(forEachfn, 'forEach')   //forEach執(zhí)行耗時(shí):201ms

function forinfn(){
  let a = []
  for(var i in arr){
    a.push(arr[i])
  }
}
clecTime(forinfn, 'forin') //forin執(zhí)行耗時(shí):2584ms (離譜)

function foroffn(){
  let a = []
  for(var i of arr){
    a.push(i)
  }
}
clecTime(foroffn, 'forof') //forof執(zhí)行耗時(shí):221ms

//  ...其余可自行測(cè)試