es6 filter() 数组过滤方法总结

1.创建一个数组，判断数组中是否存在某个值

var newarr = [
  { num: , val: 'ceshi', flag: 'aa' },
  { num: , val: 'ceshi2', flag: 'aa2'  }
]
console.log(newarr.filter(item => item.num=== ))

2.也可以通过上面方法过滤掉num为2的留下num为1的

var newarr = [
  { num: , val: 'ceshi', flag: 'aa' },
  { num: , val: 'ceshi2', flag: 'aa2'  }
]
console.log(newarr.filter(item => item.num!= ))

3.去掉空数组空字符串、undefined、null

var arr = ['','',undefined, '3.jpg',undefined]
var newArr = arr.filter(item => item)
console.log(newArr)

var arr = ['','',null, '3.jpg',null]
var newArr = arr.filter(item => item)
console.log(newArr)

>//空字符串里面不能包含空格
var arr = ['','','', '3.jpg','']
var newArr = arr.filter(item => item)
console.log(newArr)

4.去掉数组中不符合项

var arr = [,,, ,]
var newArr = arr.filter(item => item>)
console.log(newArr)

5.过滤不符合项

var arr = ['','','','','']
var newArr = arr.filter(item => item.indexOf('')<)
console.log(newArr)

6.数组去重

var arr = [, , , , , , , , , ,,,,,,,,,];
var arr2 = arr.filter((x, index,self)=>self.indexOf(x)===index)
console.log(arr2); //[1, 2, 3, 4, 5, 6, 7, 8, 0, 56]

7.数组去重es6

var arr=[,,,'',null,null,undefined,undefined,NaN,NaN]
let res=Array.from(new Set(arr));//{1,2,"1",null,undefined,NaN}
//or
let newarr=[...new Set(arr)]

8.数组对象去重es6

let person = [
     {id: 0, name: "小明"},
     {id: 1, name: "小张"},
     {id: 2, name: "小李"},
     {id: 3, name: "小孙"},
     {id: 1, name: "小周"},
     {id: 2, name: "小陈"},
];

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);
// (4) [{…}, {…}, {…}, {…}]0: {id: 0, name: "小明"}1: {id: 1, name: "小张"}2: {id: 2, name: "小李"}3: {id: 3, name: "小孙"}length: 4__proto__: Array(0)