红皮书（5）：面向对象的程序设计

2024年1月2日 111次阅读来源: 小渝人儿

建立对象

工场形式

function createPerson(name, age,job){
    var o = new object();
    o.name = name;
    o.age = age;
    o.job = job;
    o.sayName = function(){
        console.log(this.name);
    }

    return o;
}

var person1 = createPerson("Nicholas", 29, "Software Engineer");
var person2 = createPerson("Greg", 27, "Doctor");

工场形式虽然处理了建立多个类似对象的题目，但却没有处理对象辨认的题目（即如何晓得一个对象的范例）。

组织函数形式

function Person(name,age,job){
    this.name = name;
    this.age = age;
    this.job = job;
    this.sayName = function(){
        console.log(this.name);
    }
}

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");

组织函数的题目

function Person(name,age,job){
    this.name = name;
    this.age = age;
    this.job = job;
    this.sayName = new Function("console.log(this.name)"); // 与声明函数在逻辑上是等价的
}

以这类要领建立函数，会致使差别的作用域链和标示符剖析。差别实例上的同名函数是不相等的。

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");
console.log(person1.sayName == person2.sayName); // false

然后，建立两个完成一样使命的Function实例确实没有必要；何况有this对象在，基础不用在实行代码前就把函数绑定到特定对象上面。因而，大可像下面如许，经由过程把函数定义转移到组织函数外部来处理这个题目。

function Person(name, age,job){
    this.name = name;
    this.age = age;
    this.job = job;
    this.sayName = sayName;
}

function sayName(){
    console.log(this.name);
}

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");

但是新题目又来了：在全局作用域中定义的函数实际上只能被某个对象挪用，这让全局作用域有点有名无实。而更让人没法接收的是：如果对象须要定义许多要领，那末就要定义许多多个全局函数，因而我们这个自定义的援用范例就涓滴没有封装性可言了。幸亏，这些题目能够经由过程运用原型形式来处理。

原型形式

function Person(){}

Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software  Engineer";
Person.prototype.sayName = function(){
    console.log(this.name);
}

var person1 = new Person();
person1.sayName(); // Nicholas

var person2 = new Person();
person2.sayName(); // Nicholas
console.log(person1.sayName == person2.sayName);

isPrototypeOf()

console.log(Person.prototype.isPrototypeOf(person1)); // true
console.log(Person.prototype.isPrototypeOf(person2)); // true

hasOwnProperty()

function Person(){}

Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software  Engineer";
Person.prototype.sayName = function(){
    console.log(this.name);
}

var person1 = new Person();
var person2 = new Person();

console.log(person1.hasOwnProperty("name")); // false

person1.name = "Greg";
console.log(person1.name); // Greg
console.log(person1.hasOwnProperty("name")); // true

console.log(person2.name); // Nicholas
console.log(person2.hasOwnProperty("name")); // false

delete person1.name;
console.log(person1.name); // Nicholas
console.log(person1.hasOwnProperty("name")); // false

原型与in操作符

function Person(){}

Person.prototype.name = "Nicholas";
Person.prototype.age = 29;
Person.prototype.job = "Software  Engineer";
Person.prototype.sayName = function(){
    console.log(this.name);
}

var person1 = new Person();
var person2 = new Person();

console.log(person1.hasOwnProperty("name")); // false
console.log("name" in person1); // true

person1.name = "Greg";
console.log(person1.name); // Greg
console.log(person1.hasOwnProperty('name')); // true
console.log("name" in person1); // true


console.log(person2.name); // Nicholas
console.log(person2.hasOwnProperty('name')); // false
console.log("name" in person2); // true

delete person1.name;
console.log(person1.name); // Nicholas
console.log(person1.hasOwnProperty('name')); // false
console.log("name" in person1); // true

同时运用hasOwnProperty()要领和in操作符，就能够肯定该属性究竟是存在于对象中，照样存在于原型中，以下：

function hasPrototypeProperty(object,name){
    return !object.hasOwnProperty(name)&&(name in object);
}

只需in操作符返回true而hasOwnProperty()返回false,就能够肯定属性是原型中的属性。

更简朴的原型语法

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

如果constructor的值真的很主要，能够像下面如许特地将它设置回恰当的值。

function Person(){}

Person.prototype = {
    constructor: Person,
    name: "Nicholas", 
    age:29,
    job: "Software Engineer",
    sayName: function(){
        console.log(this.name);
    }
}

原型对象的题目

function Person(){}

Person.prototype = {
    constructor: Person,
    name: "Nicholas", 
    age:29,
    job: "Software Engineer",
    friends: ['Shelby', "Court"],
    sayName: function(){
        console.log(this.name);
    }
}

var person1 = new Person();
var person2 = new Person();

person1.friends.push("Van");

console.log(person1.friends); //Shelby,Court,Van
console.log(person2.friends); //Shelby,Court,Van
console.log(person1.friends===person2.friends); // true

如果我们的初志就是像如许在一切实例中同享一个数组，那末对这个效果无话可说。但是，实例平常都是要有属于本身的悉数属性的。而这个题目恰是我们很少看到有人零丁运用原型形式的缘由地点。

组合运用组织函数形式和原型形式

function Person(name,age,job){
    this.name = name;
    this.age = age;
    this.job = job;
    this.friends = ["Shelby", "Court"];
}

Person.prototype = {
    constructor: Person,
    sayName: function(){ console.log(this.name);}
}

var person1 = new Person("Nicholas", 29, "Software Engineer");
var person2 = new Person("Greg", 27, "Doctor");

person1.friends.push("Van");
console.log(person1.friends); // Shelby, Count, Van
console.log(person2.friends); // Shelby, Count
console.log(person1.friends === person2.friends); // false
console.log(person1.sayName === person2.sayName); // true

在这个例子中，实例属性都是在组织函数中定义的，而由一切实例同享的属性constructor和要领sayName()则是在原型中定义的。这类组织函数与原型混成的形式，是现在认同度最高的一种建立自定义范例的要领。

动态原型形式

function Person(name, age,job){
    this.name = name;
    this.age = age;
    this.job = job;
}

if (typeof this.sayName!='function'){
    Person.prototype.sayName = function(){
        console.log(this.name);
   }
}

var friend = new Person("Nicholas",29,"Software Engineer");
friend.sayName(); //Nicholas

寄生组织函数形式

function Person(name,age,job){
    var o = new Object();
    o.name = name;
    o.age = age;
    o.job = job;
    o.sayName = function(){
        console.log(this.name);
    };
    return o;
}

var friend = new Person("Nicholas", 29, "Software Engineer");
friend.sayName(); // Nicholas

关于寄生组织函数形式，返回的对象与组织函数或许组织函数的原型属性之间没有关系；也就是说，组织函数返回的对象与在组织函数外部建立的对象没有什么差别。

继续

原型链

function SuperType(){
     this.property= true;
}

SuperType.prototype.getSuperValue = function(){
    return this.property;
};

function Subtype(){
    this.subproperty = false;
}

// 继续了SuperType
Subtype.prototype = new SuperType();

Subtype.prototype.getSubValue = function(){
    return this.subproperty;
}

var instance = new Subtype();
console.log(instance.getSuperValue()); // true

郑重地定义要领

function SuperType(){
     this.property= true;
}

SuperType.prototype.getSuperValue = function(){
    return this.property;
};

function Subtype(){
    this.subproperty = false;
}

// 继续了SuperType
Subtype.prototype = new SuperType();

Subtype.prototype = {
    getSubValue: function(){
        return this.subproperty;
    },
    someOtherMethod: function(){
        return false;
    }
};

var instance = new Subtype();
console.log(instance.getSuperValue()); // error

原型链的题目

包括援用范例值的原型属性会被一切实例同享；而这也恰是为何要在组织函数中，而不是在原型对象中定义属性的缘由。
在建立子范例的实例时，不能向超范例的组织函数中通报参数。实际上，应当说是没有办法在不影响一切对象实例的情况下，给超范例的组织函数通报参数。

借用组织函数

function SuperType(){
    this.colors = ["red", "blue", "green"];
}

function Subtype(){
    SuperType.call(this);
}

var instance1 = new Subtype();
instance1.colors.push("black");
console.log(instance1.colors); // red, blue, green, black

var instance2 = new Subtype();
console.log(instance2.colors); // red, blue, green

通报参数

function SuperType(name){
    this.name = name;
}

function Subtype(){
    SuperType.call(this,"Nicholas");
    this.age = 29;
}

var instance = new Subtype();
console.log(instance.name); //Nicholas
console.log(instance.age); // 29

组合继续

function SuperType(name){
    this.name = name;
    this.colors = ["red", "blue", "green"];
}

SuperType.prototype.sayName = function(){
    console.log(this.name);
};

function Subtype(name,age){
    SuperType.call(this,name);
    this.age = age;
}

Subtype.prototype = new SuperType();
Subtype.prototype.sayAge = function(){
   console.log(this.age);
};

var instance1 = new Subtype("Nicholas", 29);
instance1.colors.push("black");
console.log(instance1.colors); // red, blue, green, black
instance1.sayName(); // Nicholas
instance1.sayAge(); //29

var instance2 = new Subtype("Greg", 2);
console.log(instance2.colors); // red, blue, green
instance2.sayName(); // Greg
instance2.sayAge(); //2

组合继续避免了原型链和借用函数的缺点，融会了它们的长处，成为Javascript中最经常使用的继续形式。

原型式继续

function object(o){
    function F(){}
    F.prototype = o;
    return new F();
}

var person = {
    name:"Nicholas",
    friends:["Shelby", "Court", "Van"]
};

var anotherPerson = object(person);
anotherPerson.name = "Greg";
anotherPerson.friends.push("Rob");

var yetAnotherPerson = object(person);
yetAnotherPerson.name = "Linda";
yetAnotherPerson.friends.push("Barbie");

console.log(person.friends); // Shelby, Court, Van, Rob, Barbie

Object.create()

Object.create()要领范例了原型式继续。

var person = {
    name:"Nicholas",
    friends:["Shelby", "Court", "Van"]
};

var anotherPerson = Object.create(person);
anotherPerson.name = "Greg";
anotherPerson.friends.push("Rob");

var yetAnotherPerson = Object.create(person);
yetAnotherPerson.name = "Linda";
yetAnotherPerson.friends.push("Barbie");

console.log(person.friends); // Shelby, Court, Van, Rob, Barbie

寄生式继续

function object(o){
    function F(){}
    F.prototype = o;
    return new F();
}

function inheritPrototype(subType,superType){
    var prototype = object(superType.prototype);
    prototype.constructor = subType;
    subType.prototype = prototype;
}

function SuperType(name){
    this.name = name;
    this.colors = ["red", "blue", "green"];
}

SuperType.prototype.sayName = function(){
    console.log(this.name);
}

function Subtype(name,age){
    SuperType.call(this,name);
    this.age = age;
}

inheritPrototype(Subtype, SuperType);

Subtype.prototype.sayAge = function(){
    console.log(this.age);
}

    原文作者：小渝人儿
    原文地址: https://segmentfault.com/a/1190000000376104
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