交集并集差集

  let a = new Set([1, 23, 5, 6, 7])

        let b = new Set([1, 5, 2, 3])

        console.log(a.has(1)); //查找

        //并集

        console.log([...a, ...b]);

        //交集

        console.log(

            new Set(

                [...a].filter(item => b.has(item))

            )

        );

        //差集

        console.log(

            new Set(

                [...a].filter(item => !b.has(item))

            )

        );

        let obj = {

            name: "张三",

            age: 32

        }

        console.log(obj.valueOf());

        console.log(Object.values(obj));

        console.log(Object.keys(obj));

        console.log(obj);

        //我希望字符串中有一个倒序字符串的方法

        String.prototype.myReverse = function () {

            for (var i = this.length - 1; i >= 0; i--) {

                console.log(this[i]);

            }

        };

        var str = "abcdefg";

        str.myReverse();

        console.log(str)

        //对象添加原型方法

        Object.prototype.fangfa =() =>{

            return 1111

        }

        console.log(obj);