常用的数据操作

1. a、b两个数组的交集与差集

let a = new Set([1,2,3,4,5,6])
let b = new Set([4,5,6,7,8,9])
let inter = new Set(Array.from(new Set([...b].filter(x => a.has(x)))))// a与b的交集
let differ = Array.from(new Set([...b].filter(x => !inter.has(x))))// b与inter差集/也可以理解为b去掉a的集合
<!--a与b的交集-->
console.log(inter)
{4, 5, 6}
<!--b与inter差集-->
console.log(differ)
[7, 8, 9]

2. 筛选出数组中符合条件的元素列表

let attr = [{name:1,status:1},{name:2,status:2},{name:3,status:3}]
let newList = attr.filter(item => {
return item.status === 1
})
console.log(newList)
[{name:1,status:1}]

3. 筛选出数组中符合条件的元素

- 返回符合条件的元素
  let attr = [{name:1,status:1},{name:2,status:2},{name:3,status:3}]
  let obj = attr.find(item => {
  return item.status === 1
  })
  console.log(obj)
  {name:1,status:1}
- 返回符合条件元素的位置
  var fruits = ["Banana", "Orange", "Apple", "Mango"];
  var a = fruits.indexOf("Apple");
  console.log(a)
  2
- 返回符合条件元素的位置 2
  var fruits = ["Banana", "Orange", "Apple", "Mango"];
  var a = fruits.findIndex((value)=>value=='Banana');
  console.log(a)
  0

4. 取出数组的元素属性 拼成新数组（字符串）

principalFn (list) {
  let l = list.map((li) => {
    return li.name
  })
  return l.join()
}

5. 判断数组中是否包含某一个元素

- 简单数组
  let a = [1,2,3,4,5,6,7]
  let key1 = a.includes(1)
  let key2 = a.includes(999)
  console.log(key1)
  true
  console.log(key2)
  false
- 包含对象元素的数组
  let a = [{a:1},{a:2},{a:3},{a:4},{a:5},{a:6},{a:7}]
  let num1 = a.some(item =>{
  	return item.a>3
  })
  let num2 = a.some(item =>{
  	return item.a>9
  })
  console.log(num1)
  true
  console.log(num2)
  false

6. 数组去重

• 数组内是字符串、数字、布尔值、undefined、null

let attr = [1,2,3,4,'1','2','3','4',1,2,3,4,'1','2','3','4',undefined,undefined,undefined,null,null,null]
console.log(new Set(attr)) // Set(10){1, 2, 3, 4, "1", "2", "3", "4", undefined, null}
console.log(Array.from(new Set(attr))) // [1, 2, 3, 4, "1", "2", "3", "4", undefined, null]
console.log(...new Set(attr)) // 1 2 3 4 "1" "2" "3" "4" undefined null

• 数组内是对象

let person  = [{id:1,status:1},{id:2,status:2},{id:3,status:3},{id:1,status:1},{id:1,status:4},{id:5,status:5}]
let obj = {};

let peon = person.reduce((cur,next) => {
    obj[next.id] ? "" : obj[next.id] = true && cur.push(next);
    return cur;
},[]) //设置cur默认类型为数组，并且初始值为空的数组
console.log(peon);
// [{id:1,status:1},{id:2,status:2},{id:3,status:3},{id:5,status:5}]

• 数组去重合并

let a = [1,2,3,4,56,9]
let b = [1,2,3,4,100]
console.log(new Set([...a,...b]))
// {1, 2, 3, 4, 56, 9, 100}

7. 数组对象排序

var person = [{name:"Rom",age:12},{name:"Bob",age:22},{name:"Ma",age:5},{name:"Tony",age:25}]
person.sort((a,b)=>{ return a.age-b.age})//改变原数组-升序-age字段
person.sort((a,b)=>{ return b.age-a.age})//改变原数组-降序-age字段