Summary of ES6 filter() array filtering methods

es6 filter() Summary of array filtering methods

1. Create an array , Determine whether there is a value in the array

var newarr = [
  {
     num: 1, val: 'ceshi', flag: 'aa' },
  {
     num: 2, val: 'ceshi2', flag: 'aa2'  }
]
console.log(newarr.filter(item => item.num===2 ))

2. It can also be filtered out by the above method num by 2 Of them num by 1 Of

var newarr = [
  {
     num: 1, val: 'ceshi', flag: 'aa' },
  {
     num: 2, val: 'ceshi2', flag: 'aa2'  }
]
console.log(newarr.filter(item => item.num!=2 ))

3. Remove the empty array, empty string 、undefined、null

var arr = ['1','2',undefined, '3.jpg',undefined]
var newArr = arr.filter(item => item)
console.log(newArr)

var arr = ['1','2',null, '3.jpg',null]
var newArr = arr.filter(item => item)
console.log(newArr)

>// Empty string cannot contain spaces 
var arr = ['1','2','', '3.jpg','']
var newArr = arr.filter(item => item)
console.log(newArr)

4. Remove non conformances from the array

var arr = [20,30,50, 96,50]
var newArr = arr.filter(item => item>40)  
console.log(newArr)

5. Filter nonconformities

var arr = ['10','12','23','44','42']
var newArr = arr.filter(item => item.indexOf('2')<0) 
console.log(newArr)

6. Array weight removal

var arr = [1, 2, 2, 3, 4, 5, 5, 6, 7, 7,8,8,0,8,6,3,4,56,2];
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. Array weight removal es6

var arr=[1,2,1,'1',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. Array object de duplication es6

let person = [
     {
    id: 0, name: " Xiao Ming "},
     {
    id: 1, name: " Xiao Zhang "},
     {
    id: 2, name: " petty thief "},
     {
    id: 3, name: " Little grandson "},
     {
    id: 1, name: " Xiaozhou "},
     {
    id: 2, name: " Xiao Chen "},   
];

let obj = {
    };

let peon = person.reduce((cur,next) => {
    
    obj[next.id] ? "" : obj[next.id] = true && cur.push(next);
    return cur;
},[]) // Set up cur The default type is array , And an array with an empty initial value 
console.log(peon);
// (4) [{…}, {…}, {…}, {…}]0: {id: 0, name: " Xiao Ming "}1: {id: 1, name: " Xiao Zhang "}2: {id: 2, name: " petty thief "}3: {id: 3, name: " Little grandson "}length: 4__proto__: Array(0)