详解vue数组遍历方法forEach和map的原理解析和实际应用

var a = [1,2,3,4,5]
var b = a.forEach((item) => {
  item = item * 2
})
console.log(b)
// undefiined

var a = [1,2,3,4,5]
a.forEach((item) => {
  item = item * 2
})
console.log(a)
// [1,2,3,4,5]

var a = [1,'1',{num:1},true]
a.forEach((item, index, arr) => {
  item = 2
})
console.log(a)
// [1,'1',{num:1},true]

var a = [1,'1',{num:1},true]
a.forEach((item, index, arr) => {
  item.num = 2
  item = 2
})
console.log(a)
// [1,'1',{num:2},true]

var a = [1,2,3,4,5]
a.forEach((item, index, arr) => {
  arr[index] = item * 2
})
console.log(a)
// [2,4,6,8,10]

// utils.js
const formatTime = date => {
  var newDate = new Date();
  newDate.setTime(date * 1000);
  const year = newDate.getFullYear()
  const month = newDate.getMonth() + 1
  const day = newDate.getDate()
  const hour = newDate.getHours()
  const minute = newDate.getMinutes()
  const second = newDate.getSeconds()
 
  return [year, month, day].map(formatNumber).join('-') + ' ' + [hour, minute, second].map(formatNumber).join(':')
}

const formatNumber = n => {
  n = n.toString()
  return n[1] ? n : '0' + n
}

export {
  formatTime
}

// 得到的数据格式
[
  {add_time: 1541495677, balance: 14, bn: "300708", cprice: "12.39"}
]

// index.vue
import axios from 'axios'
import { formatTime } from '@/lib/utils'
export default {
  data() {
    dataList: []
  },
  methods: {
    getData() {
     axios.get('/user?ID=12345')
     .then(function (res) {
       if(res.code == 200) {
        res.data.forEach((item) => {
          item.add_time = formatTime(item.add_time)
        }
        this.dataList = res.data
       }
     })
     .catch(function (err) {
      console.log(err);
     });
    }
  }
}

var a = [1,2,3,4,5]
var b = a.map((item) => {
  return item = item * 2
})
console.log(a) // [1,2,3,4,5]
console.log(b) // [2,4,6,8,10]

export default {
  data() {
    moneyList: [1000,2000,5000,10000,20000,50000]
  },
  computed: {
    moneyList_new() {
      return this.moneyList.map((item) => {
        const random = Math.random() > 0.5 ? 1 : -1;
        return Math.floor(Math.random()*100) * random + item;
      })
    }
  }
}