数组变换

map：n变n

let arr = [0,1,2,2,3,3,3,4,4,4,4,6]
let arr2 = arr.map(补全代码)
console.log(arr2)

将代码转换成 ['周日', '周一', '周二', '周二', '周三', '周三', '周三', '周四', '周四', '周四', '周四','周六']

let arr = [0,1,2,2,3,3,3,4,4,4,4,6]
let arr2 = arr.map((item)=>{
  let week =['周日', '周一', '周二', '周三', '周四', '周五', '周六']
  return week[item]
})
或者：
let arr2 = arr.map((item)=> {
return {
0: '周日', 1: '周一', 2: '周二', 3: '周三', 4: '周四', 5: '周五',6: '周六'
}[item]
})

filter:n变少

let scores = [95,91,59,55,42,82,72,85,67,66,55,91]
let scores2 = scores.filter(补全代码)
console.log(scores2) //  [95,91,82,72,85,67,66, 91]

找出所有大于 60 分的成绩

let scores = [95,91,59,55,42,82,72,85,67,66,55,91]
let scores2 = scores.filter(item=> item - 60>0)
console.log(scores2)
或者
let scores = [95,91,59,55,42,82,72,85,67,66,55,91]
let scores2 = scores.filter(item=>item>60?)
console.log(scores2)

reduce：n变一

let scores = [95,91,59,55,42,82,72,85,67,66,55,91]
let sum = scores.reduce((sum, n)=>{
  补全代码
},0)
console.log(sum) // 奇数之和：598

算出所有奇数之和

let scores = [95,91,59,55,42,82,72,85,67,66,55,91]
let sum = scores.reduce((sum, n)=>{
  if(n%2===1){
        return sum+n
}else{
   return sum
}},0)
或者：
let sum = scores.reduce((sum, n)=>{
  return n%2===0 ? sum : sum+n},0)