对象常用操作方法

//delete方法是从对象中删除键值对

        delete obj.cname;

                console.log(obj);//{age: 18}

        //in 判断对象是否包含一个 语法：key in obj  返回一个布尔值

        console.log("age" in obj) //true

        //for in 快速遍历

        var obj2 = {

            age:18,

            add:"中国",

            cname:"凉白开"

        }

        for(var i in obj2) {

            console.log(i) // key

            console.log(obj2[i]) //输出值

        }