1.forEach

let arr = [‘aaa‘, ‘bbb‘, ‘ccc‘]
arr.forEach((item, index, array) => {
    console.log(val, index, arr)
})

類似於，for循環

2.map

正常情況下，需要配合return來返回一個新的數組，如果沒有return， 則相當於forEach

let arr = [
      {name: ‘小明‘, sex: ‘男‘, age: 15},
      {name: ‘小紅‘, sex: ‘女‘, age: 13},
      {name: 
 
‘小東‘, sex: ‘男‘, age: 17},
      {name: ‘小強‘, sex: ‘男‘, age: 14}
    ]
let newArr = arr.map((item, index, array) => {
      if (item.age > 16) {
        return item.name + ‘已成年‘
      } else {
        return item.name + ‘未成年‘
      }
})
console.log(newArr)

3.filter

過濾， 返回一個新的數組

let arr = [
      {name: ‘小明‘, sex: ‘男‘, age: 15},
      {name: ‘小紅‘, sex: ‘女‘, age: 13},
      {name: ‘小東‘, sex: ‘男‘, age: 17},
      {name: ‘小強‘, sex: ‘男‘, age: 14}
    ]
let newArr = arr.filter((item, index, array) => {return item.age < 16
})
console.log(newArr)

4.some

按照我的理解就是判斷數組中是否有滿足條件的項

let arr = [
    {name: ‘小明‘, sex: ‘男‘, age: 15},
    {name: ‘小紅‘, sex: ‘女‘, age: 13},
    {name: ‘小東‘, sex: ‘男‘, age: 17},
    {name: ‘小強‘, sex: ‘男‘, age: 14}
]
let newArr = arr.some((item, index, array) => {
    return item.age < 16
})
console.log(newArr)

5.every

判斷數組中是否每一項都滿足條件

let arr = [
    {name: ‘小明‘, sex: ‘男‘, age: 15},
    {name: ‘小紅‘, sex: ‘女‘, age: 13},
    {name: ‘小東‘, sex: ‘男‘, age: 17},
    {name: ‘小強‘, sex: ‘男‘, age: 14}
]
let newArr = arr.every((item, index, array) => {
    return item.age < 16
})
console.log(newArr)

6.reduce

類似於遞歸函數，從左往右循環

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
let res = arr.reduce((prev, cur, index, array) => {
    return prev + cur
})
console.log(res)

7、reducerRight

類似於遞歸函數，從右往左循環

es5 數組新增加的方法