es6 filter数组过滤方法

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.数组去重

   var chognfu = [1,2,4,1,10,4,3,21]
      var self = [] //去重之后数组
      chognfu.filter((item)=>{
        if(self.indexOf(item)==-1){
          self.push(item)
        }
      })
      console.log(self,'self')