js filter() es6 方法总结

1 创建一个数组，判断数组中是否存在某个值

let a = [1, 2, 3]; 
a.includes(2); 

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

<script type="text/javascript">
    var array = ["1","2","3","4"];
    alert(aray.indexOf(String(2)));
        alert(array.indexOf(5));
</script>
<script type="text/javascript">
     var array = [1,2,3,4];
     alert(array.indexOf(2));
     alert(array.indexOf(5));
</script>
var arr = ['1','2',undefined, '3.jpg',undefined]      
var newArr = arr.filter((element, index, array)=>{
    if(element==1){
        return element;
    }
 })
console.log(newArr)

2去掉空数组空字符串、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)

>//空字符串里面不能包含空格
var arr = ['1','2','', '3.jpg','']
var newArr = arr.filter(item => item)
console.log(newArr)

3.去掉数组中不符合项

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

4.过滤不符合项

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

数组去重

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]