Javascript 为什么getter返回旧值

我有以下代码：

function User(fullName) {
    this.fullName = fullName;
    Object.defineProperties(this,
        {
            firstName: {
                get: function () {
                    return fullName.split(" ")[0];
                }
                ,
                set: function (fName) {
                    this.fullName = fName + " " + this.lastName;
                }
            },
            lastName: {
                get: function () {
                    return fullName.split(" ")[1];
                }
                ,
                set: function (lName) {
                    this.fullName = this.firstName + " " + lName;
                }
            }
        })

}

以及要执行的以下代码：

var vasya = new User("oldName oldSurname");

console.log(vasya.firstName); // 


vasya.firstName = "newName";
vasya.lastName = "newSurname"

console.log(vasya.fullName);

这将输出

newName-oldnamname

如果要稍微更改它：

var vasya = new User("oldName oldSurname");

console.log(vasya.firstName); //
console.log(vasya.lastName); //

vasya.firstName = "newName";
vasya.lastName = "newSurname"

console.log(vasya.fullName);

它返回

oldName newSurname

---

请解释为什么我现在看到的是

oldName

而不是

newName

我玩了这段代码，发现是命名冲突。 这种变体工作正常

function User(fullNameValue) {
    this.fullName = fullNameValue; // renamed function argument
    Object.defineProperties(this,
        {
            firstName: {
                get: function () {
                    return this.fullName.split(" ")[0];//I use this here. without it I returned function argument
                }
                ,
                set: function (fName) {
                    this.fullName = fName + " " + this.lastName; 
                }
            },
            lastName: {
                get: function () {
                    return this.fullName.split(" ")[1];//I use this here. without it I 
                }
                ,
                set: function (lName) {
                    this.fullName = this.firstName + " " + lName;
                }
            }
        })

}

引用fullNameValue时必须使用“this”关键字，否则它将使用作为param传递的变量

function User(fullName) {
    this.fullName = fullName;
    Object.defineProperties(this,
    {
        firstName: {
            get: function () {
                return this.fullName.split(" ")[0];
            }
            ,
            set: function (fName) {
                this.fullName = fName + " " + this.lastName;
            }
        },
        lastName: {
            get: function () {
                return this.fullName.split(" ")[1];
            }
            ,
            set: function (lName) {
                this.fullName = this.firstName + " " + lName;
            }
        }
    })

}