对象的函数解构

直接把这个JSON格式数据当作参数，传递到函数内部进行处理

        let JSON = {
            a:'jie',
            b:'杰'
        }
        function fun({a,b}){
            console.LOG(a,b);
        }
        fun(json) //jie 杰

数组的函数解构

       let arr =['jie','biao','nine'];
        function fun(a,b,c){
            console.log(a,b,c)
        }
        fun(...arr)  //jie biao nine

in

in是用来判断对象或者数组中是否存在某个值的

对象

        let obj={
            a:'jie'
        }
        console.log('a' in obj) // true
        console.log('b' in obj) //false

数组

这里的0指的是数组下标位置是否为空。

        let arr = [,,,];
        console.log(0 in arr);  //false

        let arr2 = ['jie','bioa'];
        console.log(0 in arr2) //true
        console.log('jie' in arr2) //false

map

        VAR arr2 = ['jie', 'bioa', 'nine'];
        console.log(arr2.map(item => {
            return item = "web"
        })) (3) ["web", "web", "web"]
         console.log(arr2.map(val => "web")) //(3) ["web", "web", "web"]

数组转为字符串

join

        var arr2 = ['jie', 'bioa', 'nine'];
        console.log(arr2.join('|'))   //jie|bioa|nine

toString

        var arr2 = ['jie', 'bioa', 'nine'];
        console.log(arr2.toString()) //jie,bioa,nine