技術標籤：陣列concat

拿到後臺返回的陣列物件格式的資料

data = [
  {name: "n1", "email": "[email protected]"},
  {name: "n2",   "email": "[email protected]"},
  {name: "n3",  "email": "[email protected]"}
];

前端對這種資料做判斷、整合的時候有很多方便的方法

1. Object.keys()取出物件所有屬性名 返回陣列
2. Object.values()取出物件所有值 返回陣列
3. arr.reduce（）；陣列求和 求乘積 很方便
4. map()

arr.reduce(function(prev, cur, index, arr) {
    console.log(prev, cur, index);
    return prev + cur;
})

var  arr = [1, 2, 3, 4];
var sum = arr.reduce((x,y)=>x+y)
var mul = arr.reduce((x,y)=>x*y)
console.log( sum ); //求和，10
console.log( mul ); //求乘積，24
 

計算陣列出現次數

let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice'];

let nameNum = names.reduce((pre,cur)=>{
  if(cur in pre){
    pre[cur]++
  }else{
    pre[cur] = 1 
  }
  return pre
},{})
console.log(nameNum); //{Alice: 2, Bob: 1, Tiff: 1, Bruce: 1}

陣列去重

let arr = [1,2,3,4,4,1]
let newArr = arr.reduce((pre,cur)=>{
    if(!pre.includes(cur)){
      return pre.concat(cur)
    }else{
      return pre
    }
},[])
console.log(newArr);// [1, 2, 3, 4]
 

二維陣列轉化

let arr = [[0, 1], [2, 3], [4, 5]]
let newArr = arr.reduce((pre,cur)=>{
    return pre.concat(cur)
},[])
console.log(newArr); // [0, 1, 2, 3, 4, 5]

多維陣列轉化

let arr = [[0, 1], [2, 3], [4,[5,6,7]]]
const newArr = function(arr){
   return arr.reduce((pre,cur)=>pre.concat(Array.isArray(cur)?newArr(cur):cur),[])
}
console.log(newArr(arr)); //[0, 1, 2, 3, 4, 5, 6, 7]

物件屬性求和

var result = [
    {
        subject: 'math',
        score: 10
    },
    {
        subject: 'chinese',
        score: 20
    },
    {
        subject: 'english',
        score: 30
    }
];

var sum = result.reduce(function(prev, cur) {
    return cur.score + prev;
}, 0);
console.log(sum) //60

map() map方法的作用不難理解，“對映”，也就是原陣列被“對映”成對應新陣列。

可以很方便的將物件陣列映射出值

var users = [
  {name: "張含韻", "email": "[email protected]"},
  {name: "江一燕",   "email": "[email protected]"},
  {name: "李小璐",  "email": "[email protected]"}
];

var emails = users.map(function (user) { return user.email; });

console.log(emails.join(", ")); // [email protected], [email protected], [email protected]