# 数组方法

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## reduce

### 累加

``````var arr1 = [1, 2, 3, 4]
// var result1 = arr.reduce((prev, next) => {
//   return prev + next
// }, 0)

var result1 = arr1.reduce((prev, next) => {
return prev + next
})
console.log('result1', result1)

### 累乘

``````var arr2 = [1, 2, 3, 4]
var result2 = arr2.reduce((prev, next) => {
return prev * next
}, 1)
console.log('result2', result2)

### 数组去重

``````var arr3 = [1, 2, 2, 3, 4]
var result3 = arr3.reduce((prev, next) => {
if (!prev.includes(next)) {
return [...prev, next]
} else {
return prev
}
}, [])

``````for (let i = 0; i < arr3.length; i++) {
if (!res.includes(arr3[i])) {
res.push(arr3[i])
} else {
continue
}
}

### 最大值/最小值

``````var arr4 = [1, 2, 3, 4]
var result4 = arr4.reduce((prev, next) => {
if (prev > next) {
return prev
} else {
return next
}
})
var result4 = arr4.reduce((prev, next) => {
return prev > next ? prev : next
})
console.log('result4', result4)

``````let max = arr4[0]
for (let i = 0; i < arr4.length; i++) {
if (arr4[i] > max) {
max = arr4[i]
}
}

### 扁平化

``````function Flat (arr = []) {
return arr.reduce((prev, next) => {
if (Array.isArray(next)) {
return prev.concat(Flat(next))
} else {
return prev.concat(next)
}
}, [])
}

``````function Flat (arr) {
var res = []
for (let i = 0; i < arr.length; i++) {
if (Array.isArray(arr[i])) {
res = res.concat(Flat(arr[i]))
} else {
res.push(arr[i])
}
}
return res
}

## map

### 单数组

``````var arr1 = [1, 2, 3, 4]
var result1 = arr1.map(item => {
return item + 1
})
console.log('result1', result1)

### 数组中包含对象

``````var arr2 = [
{
age: 1,
name: 'a'
},
{
age: 2,
name: 'b'
},
{
age: 3,
name: 'c'
}
]

var result2 = arr2.map(item => {
return {
age: item.age + 1,
name: item.name
}
})
console.log('result2', result2)
var result3 = arr2.map(item => {
return {
age: item.age + 1
}
})
console.log('arr2', arr2)
console.log('result3', result3)