// for in  依次获取对象的key
    for(key in obj){
        console.log(key) //name age sex
    }

// Object.keys  返回对象key，
    let keys= Object.keys(obj)
    console.log(keys) // ["name", "age", "sex"]

// Object.values 返回对象value，所组成的数组
    let values= Object.values(obj)
    console.log(values) //["jack", 12, "M"]

// Object.entries 返回对象[key,value] 组成的二维数组
    let entries= Object.entries(obj)
    console.log(entries)  // [["name", "jack"],["age", 12],["sex", "M"]]