一、重寫整個原型物件

用一個包含所有屬性和方法的物件字面量來重寫整個原型物件。

function Person(){
}
//更繁瑣的寫法
Person.prototype.name="Nicholas";
Person.prototype.age=29;
Person.prototype.job="SoftWare Engineer";
Person.prototype.sayName=function(){
    console.log(this.name);
};
//更簡單的寫法
Person.prototype={
    name:"Nicholas",
    age:29,
    job:
 
"SoftWare Engineer",
    sayName:function(){
    console.log(this.name);
}
};

因為本質上重寫了預設的prototype物件，constructor屬性不再預設指向Person，而變成了普通物件的constructor值，也就是指向普通物件Object.

二、優化

function Person(){
}
Person.prototype={
    name:"Nicholas",
    age:29,
    job:"SoftWare Engineer",
    sayName:function(){
 

    console.log(this.name);
}
};
var friend=new Person();
console.log(friend instanceof Object);//true
console.log(friend instanceof Person);//true
console.log(friend.constructor==Person);//false
console.log(friend.constructor==Object);//true

//修改為
function Person(){
}
Person.prototype={
    constructor:Person,
 

    name:"Nicholas",
    age:29,
    job:"SoftWare Engineer",
    sayName:function(){
    console.log(this.name);
}
};
var friend=new Person();
console.log(friend instanceof Object);//true
console.log(friend instanceof Person);//true
console.log(friend.constructor==Person);//true
console.log(friend.constructor==Object);//true

//以上面的方式重設constructor屬性會導致它的[[Enumerable]]特性被設定為true,而ES5中，原生的constructor屬性時不可列舉的。更優化版：
function Person(){
}
Person.prototype={
    constructor:Person,
    name:"Nicholas",
    age:29,
    job:"SoftWare Engineer",
    sayName:function(){
    console.log(this.name);
}
};
Object.defineProperty(Person.prototype,"constructor",{
    enumerable:false,
    value:Person
});