Does javascript support object-oriented-Front-end Q&A-php.cn

JavaScript supports object-oriented programming; object-oriented programming is a programming model that uses abstract methods to create models based on the real world. Object-oriented uses previously established paradigms, including modularity, polymorphism, and encapsulation. , many popular programming languages including JavaScript support object-oriented programming.

Does javascript support object-oriented

The operating environment of this tutorial: Windows 10 system, JavaScript version 1.8.5, Dell G3 computer.

Does JavaScript support object-oriented?

The core of JavaScript supports object-oriented, and it also provides powerful and flexible OOP language capabilities. This article starts with an introduction to object-oriented programming, takes you to explore the object model of JavaScript, and finally describes some concepts of object-oriented programming in JavaScript.

Object-oriented programming

Object-oriented programming is a programming model that uses abstract methods to create models based on the real world. It uses previously established paradigms, including modularity, polymorphism, and encapsulation. Today, object-oriented programming (OOP) is supported by many popular programming languages such as Java, JavaScript, C#, C, Python, PHP, Ruby, and Objective-C.

Compared with the traditional software design concept that "a program is just a collection of functions, or a simple list of computer instructions.", object-oriented programming can be regarded as software design that uses a series of objects to cooperate with each other. In OOP, each object can receive messages, process data and send messages to other objects. Each object can be thought of as a small independent machine with clear roles or responsibilities.

Object-oriented programming aims to promote better flexibility and maintainability in programming, and is widely popular in large-scale software projects. With its emphasis on modularity, object-oriented code development is simpler and easier to understand, making it more straightforward to analyze, code and understand complex situations and processes than non-modular programming methods.

Namespace

Namespaces allow developers to bundle all functionality of a container under a unique, application-related name.

Class Class

Defines the characteristics of the object. It is a template definition of the properties and methods of an object.

Object An instance of the object

class.

Property Property

Characteristics of the object, such as color.

Method Method

The ability of the object, such as walking.

Constructor Constructor

The method that is called when the object is initialized. Usually its name matches the class that contains it.

Inheritance

A class can inherit the characteristics of another class.

Encapsulation Encapsulation

A method of binding data and related methods together.

Abstraction

Objects that combine complex inheritance, methods, and properties can simulate realistic models.

Polymorphism

Polymorphism means "many", and morphism means "form". Different classes can define the same methods or properties.

Prototype Programming

Prototype-based programming is not a style embodied in object-oriented programming, and behavior reuse (also called inheritance in class-based languages) is achieved through Implemented by the process of decorating an existing object which serves as a prototype. This pattern is also called weak classing, prototyping, or instance-based programming.

The original (and most typical) example of a prototype-based language was developed by David Angell and Randall Smith. However, the weakly classed programming style has become increasingly popular recently and has been adopted by programming languages such as JavaScript, Cecil, NewtonScript, IO, MOO, REBOL, Kevo, Squeak (which uses frameworks to manipulate Morphic components), and several other programming languages .

JavaScript Object-Oriented Programming

Namespace

A namespace is a container that allows developers to bundle all functionality under a unique, application-specific name . In JavaScript, a namespace is just another object containing methods, properties, and objects.

Note: It is important to realize that unlike other object-oriented programming languages, there is no difference at the language level between ordinary objects and namespaces in Javascript. This can be confusing for JavaScript beginners.

The idea behind creating a JavaScript namespace is simple: a global object is created, and all variables, methods, and functions become properties of that object. Using namespaces also minimizes the possibility of name conflicts for your application.

Let’s create a global variable called MYAPP

// 全局命名空间
var MYAPP = MYAPP || {};

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In the above code example, we first check whether MYAPP has been defined (whether in the same file or in another file). If so, then use the existing MYAPP global object, otherwise, create an empty object named MYAPP to encapsulate methods, functions, variables and objects.

We can also create sub-namespaces:

// 子命名空间
MYAPP.event = {};

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The following is the code for creating namespaces and adding variables, functions and methods:

// 给普通方法和属性创建一个叫做MYAPP.commonMethod的容器
MYAPP.commonMethod = {
  regExForName: "", // 定义名字的正则验证
  regExForPhone: "", // 定义电话的正则验证
  validateName: function(name){
    // 对名字name做些操作，你可以通过使用“this.regExForname”
    // 访问regExForName变量
  },
  
  validatePhoneNo: function(phoneNo){
    // 对电话号码做操作
  }
}
 
// 对象和方法一起申明
MYAPP.event = {
    addListener: function(el, type, fn) {
    //  代码
    },
   removeListener: function(el, type, fn) {
    // 代码
   },
   getEvent: function(e) {
   // 代码
   }
   
   // 还可以添加其他的属性和方法
}
 
//使用addListener方法的写法:
MYAPP.event.addListener("yourel", "type", callback);

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Standard built-in objects

JavaScript有包括在其核心的几个对象，例如，Math，Object，Array和String对象。下面的例子演示了如何使用Math对象的random()方法来获得一个随机数。

console.log(Math.random());

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注意：这里和接下来的例子都假设名为 console.log 的方法全局有定义。console.log 实际上不是 JavaScript 自带的。

查看 JavaScript 参考：全局对象了解 JavaScript 内置对象的列表。

JavaScript 中的每个对象都是 Object 对象的实例且继承它所有的属性和方法。

自定义对象

类

JavaScript 是一种基于原型的语言，它没类的声明语句，比如 C+ + 或 Java 中用的。这有时会对习惯使用有类申明语句语言的程序员产生困扰。相反，JavaScript可用方法作类。定义一个类跟定义一个函数一样简单。在下面的例子中，我们定义了一个新类Person。

function Person() { }
// 或
var Person = function(){ }

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对象（类的实例）

我们使用 new obj 创建对象 obj 的新实例, 将结果（obj 类型）赋值给一个变量方便稍后调用。

在下面的示例中，我们定义了一个名为Person的类，然后我们创建了两个Person的实例(person1 and person2)。

function Person() { }
var person1 = new Person();
var person2 = new Person();

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注意：有一种新增的创建未初始化实例的实例化方法，请参考 Object.create 。

构造器

在实例化时构造器被调用 (也就是对象实例被创建时)。构造器是对象中的一个方法。在JavaScript中函数就可以作为构造器使用，因此不需要特别地定义一个构造器方法，每个声明的函数都可以在实例化后被调用执行。

构造器常用于给对象的属性赋值或者为调用函数做准备。在本文的后面描述了类中方法既可以在定义时添加，也可以在使用前添加。

在下面的示例中, Person类实例化时构造器调用一个 alert函数。

function Person() {
  alert(&#39;Person instantiated&#39;);
}
 
var person1 = new Person();
var person2 = new Person();

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属性 (对象属性)

属性就是类中包含的变量;每一个对象实例有若干个属性. 为了正确的继承，属性应该被定义在类的原型属性 (函数)中。

可以使用关键字 this调用类中的属性, this是对当前对象的引用。从外部存取(读/写)其属性的语法是: InstanceName.Property; 这与C++，Java或者许多其他语言中的语法是一样的 (在类中语法 this.Property 常用于set和get属性值)

在下面的示例中，我们为定义Person类定义了一个属性 firstName 并在实例化时赋初值。

function Person(firstName) {
  this.firstName = firstName;
  alert(&#39;Person instantiated&#39;);
}
 
var person1 = new Person(&#39;Alice&#39;);
var person2 = new Person(&#39;Bob&#39;);
 
// Show the firstName properties of the objects
alert(&#39;person1 is &#39; + person1.firstName); // alerts "person1 is Alice"
alert(&#39;person2 is &#39; + person2.firstName); // alerts "person2 is Bob"

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方法（对象属性）

方法与属性很相似，不同的是：一个是函数，另一个可以被定义为函数。调用方法很像存取一个属性, 不同的是add () 在方法名后面很可能带着参数。为定义一个方法, 需要将一个函数赋值给类的 prototype 属性; 这个赋值给函数的名称就是用来给对象在外部调用它使用的。

在下面的示例中，我们给Person类定义了方法 sayHello()，并调用了它。

function Person(firstName) {
  this.firstName = firstName;
}
 
Person.prototype.sayHello = function() {
  alert("Hello, I&#39;m " + this.firstName);
};
 
var person1 = new Person("Alice");
var person2 = new Person("Bob");
 
// call the Person sayHello method.
person1.sayHello(); // alerts "Hello, I&#39;m Alice"
person2.sayHello(); // alerts "Hello, I&#39;m Bob"

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在JavaScript中方法通常是一个绑定到对象中的普通函数, 这意味着方法可以在其所在context之外被调用。思考下面示例中的代码:

function Person(firstName) {
  this.firstName = firstName;
}
 
Person.prototype.sayHello = function() {
  alert("Hello, I&#39;m " + this.firstName);
};
 
var person1 = new Person("Alice");
var person2 = new Person("Bob");
var helloFunction = person1.sayHello;
 
person1.sayHello();                                 // alerts "Hello, I&#39;m Alice"
person2.sayHello();                                 // alerts "Hello, I&#39;m Bob"
helloFunction();                                    // alerts "Hello, I&#39;m undefined" (or fails with a TypeError in strict mode)
console.log(helloFunction === person1.sayHello);          // logs true
console.log(helloFunction === Person.prototype.sayHello); // logs true
helloFunction.call(person1);                        // logs "Hello, I&#39;m Alice"

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如上例所示, 所有指向sayHello函数的引用，包括 person1, Person.prototype, 和 helloFunction 等，均引用了相同的函数.

在调用函数的过程中，this的值取决于我们怎么样调用函数. 在通常情况下，我们通过一个表达式person1.sayHello()来调用函数：即从一个对象的属性中得到所调用的函数。此时this被设置为我们取得函数的对象（即person1）。这就是为什么person1.sayHello() 使用了姓名“Alice”而person2.sayHello()使用了姓名“bob”的原因。

然而我们使用不同的调用方法时, this的值也就不同了。当从变量 helloFunction()中调用的时候， this就被设置成了全局对象 (在浏览器中即window)。由于该对象 (非常可能地) 没有firstName 属性, 我们得到的结果便是"Hello, I'm undefined". (这是松散模式下的结果，在严格模式中，结果将不同（此时会产生一个error）。但是为了避免混淆，我们在这里不涉及细节) 。另外，我们可以像上例末尾那样，使用Function#call (或者Function#apply)显式的设置this的值。

更多有关信息请参考 Function#call and Function#apply

继承

创建一个或多个类的专门版本类方式称为继承（Javascript只支持单继承）。创建的专门版本的类通常叫做子类，另外的类通常叫做父类。在Javascript中，继承通过赋予子类一个父类的实例并专门化子类来实现。在现代浏览器中你可以使用 Object.create 实现继承。

JavaScript 并不检测子类的 prototype.constructor (见 Object.prototype), 所以我们必须手动申明它。

在下面的例子中, 我们定义了 Student类作为 Person类的子类。之后我们重定义了sayHello() 方法并添加了 sayGoodBye() 方法。

// 定义Person构造器
function Person(firstName) {
  this.firstName = firstName;
}
 
// 在Person.prototype中加入方法
Person.prototype.walk = function(){
  alert("I am walking!");
};
Person.prototype.sayHello = function(){
  alert("Hello, I&#39;m " + this.firstName);
};
 
// 定义Student构造器
function Student(firstName, subject) {
  // 调用父类构造器, 确保(使用Function#call)"this" 在调用过程中设置正确
  Person.call(this, firstName);
 
  // 初始化Student类特有属性
  this.subject = subject;
};
 
// 建立一个由Person.prototype继承而来的Student.prototype对象.
// 注意: 常见的错误是使用 "new Person()"来建立Student.prototype.
// 这样做的错误之处有很多, 最重要的一点是我们在实例化时
// 不能赋予Person类任何的FirstName参数
// 调用Person的正确位置如下，我们从Student中来调用它
Student.prototype = Object.create(Person.prototype); // See note below
 
// 设置"constructor" 属性指向Student
Student.prototype.constructor = Student;
 
// 更换"sayHello" 方法
Student.prototype.sayHello = function(){
  console.log("Hello, I&#39;m " + this.firstName + ". I&#39;m studying " + this.subject + ".");
};
 
// 加入"sayGoodBye" 方法
Student.prototype.sayGoodBye = function(){
  console.log("Goodbye!");
};
 
// 测试实例:
var student1 = new Student("Janet", "Applied Physics");
student1.sayHello();   // "Hello, I&#39;m Janet. I&#39;m studying Applied Physics."
student1.walk();       // "I am walking!"
student1.sayGoodBye(); // "Goodbye!"
 
// Check that instanceof works correctly
console.log(student1 instanceof Person);  // true
console.log(student1 instanceof Student); // true

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对于 “ Student.prototype = Object.create(Person.prototype); ” 这一行，在不支持 Object.create 方法的老 JavaScript 引擎中，可以使用一个 "polyfill"（又名"shim"，查看文章链接），或者使用一个 function 来获得相同的返回值，就像下面：

function createObject(proto) {
    function ctor() { }
    ctor.prototype = proto;
    return new ctor();
}
 
// Usage:
Student.prototype = createObject(Person.prototype);

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更多相关信息请参考 Object.create，连接中还有一个老JavaScript引擎的兼容方案（shim）。

封装

在上一个例子中，Student类虽然不需要知道Person类的walk()方法是如何实现的，但是仍然可以使用这个方法；Student类不需要明确地定义这个方法，除非我们想改变它。这就叫做封装，对于所有继承自父类的方法，只需要在子类中定义那些你想改变的即可。

抽象

抽象是允许模拟工作问题中通用部分的一种机制。这可以通过继承（具体化）或组合来实现。

JavaScript通过继承实现具体化，通过让类的实例是其他对象的属性值来实现组合。

JavaScript Function 类继承自Object类（这是典型的具体化）。Function.prototype的属性是一个Object实例（这是典型的组合）。

var foo = function(){};
console.log( &#39;foo is a Function: &#39; + (foo instanceof Function) );                  // logs "foo is a Function: true"
console.log( &#39;foo.prototype is an Object: &#39; + (foo.prototype instanceof Object) ); // logs "foo.prototype is an Object: true"

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多态

就像所有定义在原型属性内部的方法和属性一样，不同的类可以定义具有相同名称的方法;方法是作用于所在的类中。并且这仅在两个类不是父子关系时成立（继承链中，一个类不是继承自其他类）。