1.创建一个数组，判断数组中是否存在某个值

  // 1.创建一个数组，判断数组中是否存在某个值
                var newarr = [
                    { num: 1, val: 'ceshi111', flag: 'aa111' },
                    { num: 2, val: 'ceshi222', flag: 'aa222'  }
                ];
                var filter = newarr.filter(item => item.num===2 );
                console.log(filter)

** 2.创建一个数组，过滤掉num为2的留下num为1的**

        var newarr = [
            { num: 1, val: 'ceshi111', flag: 'aa111' },
            { num: 2, val: 'ceshi222', flag: 'aa222'  }
        ];
        var filter = newarr.filter(item => item.num!=2 );
        console.log(filter)

3 创建一个数组，去掉空数组空字符串、undefined、null

            var arr1 = ['1','2',undefined, '3.jpg',undefined]
            var newArr1 = arr1.filter(item => item)
            console.log(newArr1)

            var arr2 = ['1','2',null, '3.jpg',null]
            var newArr2 = arr2.filter(item => item)
            console.log(newArr2)
            //空字符串里面不能包含空格
            var arr3 = ['1','2','', '3.jpg','']
            var newArr3 = arr3.filter(item => item)
            console.log(newArr3)

4 创建一个数组，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 创建一个数组，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]

6 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);

7 .数组去重

     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)]
                console.log(res);