JavaScript对象原型 

所有JavaScript对象都从原型继承属性和方法

function Person(first, last, age, eye) {
        this.firstName = first;
        this.lastName = last;
        this.age = age;
        this.eyeColor = eye;
    }
    var myFather = new Person("John", "Doe", 50, "blue");
    var myMother = new Person("Sally", "Rally", 48, "green");
    document.getElementById("demo").innerHTML =
        "My father is " + myFather.age + ". My mother is " + myMother.age;

我们还了解到，您无法向现有对象构造函数添加新属性：

function Person(first, last, age, eye) {
        this.firstName = first;
        this.lastName = last;
        this.age = age;
        this.eyeColor = eye;
    }
    Person.nationality = "English";
    var myFather = new Person("John", "Doe", 50, "blue");
    var myMother = new Person("Sally", "Rally", 48, "green");
    document.getElementById("demo").innerHTML =
        "The nationality of my father is " + myFather.nationality;

要向构造函数添加新属性，必须将其添加到构造函数：

function Person(first, last, age, eye) {
        this.firstName = first;
        this.lastName = last;
        this.age = age;
        this.eyeColor = eye;
        this.nationality = "English";
    }
    var myFather = new Person("John", "Doe", 50, "blue");
    var myMother = new Person("Sally", "Rally", 48, "green");
    document.getElementById("demo").innerHTML =
        "我父亲的国籍是 " + myFather.nationality + ". 我母亲的国籍是： " + myMother.nationality;

原型继承 

所有JavaScript对象都从原型继承属性和方法： 

Object.prototype位于原型继承链的顶部：Date对象，Array对象和Person对象继承自Object.prototype。

*   Date 对象继承自 Date.prototype
*   Array 对象继承自 Array.prototype
*   Person 对象继承自 Person.prototype

向对象添加属性和方法

有时，您希望向给定类型的所有现有对象添加新属性（或方法）。有时您想要向对象构造函数添加新属性（或方法）。

使用 原型 属性

JavaScript prototype属性允许您向对象构造函数添加新属性：

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}
Person.prototype.nationality = "English";

JavaScript prototype属性还允许您向对象构造函数添加新方法：

function Person(first, last, age, eyecolor) {
  this.firstName = first;
  this.lastName = last;
  this.age = age;
  this.eyeColor = eyecolor;
}
Person.prototype.name = function() {
  return this.firstName + " " + this.lastName;
};