es6中filter()数组过滤方法的介绍（附代码）

1.创建一个数组，判断数组中是否存在某个值

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

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

3.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)

4.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)

5.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)

6.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]

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