命名空间
命名空间是一个容器，它允许开发人员在一个独特的，特定于应用程序的名称下捆绑所有的功能。 在JavaScript中，命名空间只是另一个包含方法，属性，对象的对象。
需要认识到非常重要的一点，与其他面向对象编程语言中的普通对象和命名空间相比，它们在语言层面上没有区别。
创造的JavaScript命名空间背后的想法很简单：一个全局对象被创建，所有的变量，方法和功能成为该对象的属性。使用命名空间也最大程度地减少应用程序的名称冲突的可能性。
我们来创建一个全局变量叫做 MYAPP
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<code
class
=
" language-js"
><span
class
=
"token comment"
>
// 全局命名空间
<span
class
=
"token keyword"
>
var
MYAPP <span
class
=
"token operator"
>= MYAPP <span
class
=
"token operator"
>|| <span
class
=
"token punctuation"
>{<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></span></code>
|
在上面的代码示例中，我们首先检查MYAPP是否已经被定义（是否在同一文件中或在另一文件）。如果是的话，那么使用现有的MYAPP全局对象，否则，创建一个名为MYAPP的空对象用来封装方法，函数，变量和对象。
我们也可以创建子命名空间：
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<code
class
=
" language-js"
><span
class
=
"token comment"
>
// 子命名空间
MYAPP<span
class
=
"token punctuation"
>.event <span
class
=
"token operator"
>= <span
class
=
"token punctuation"
>{<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></code>
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下面是用于创建命名空间和添加变量，函数和方法的代码写法：
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<code
class
=
" language-js"
><span
class
=
"token comment"
>
// 给普通方法和属性创建一个叫做MYAPP.commonMethod的容器
MYAPP<span
class
=
"token punctuation"
>.commonMethod <span
class
=
"token operator"
>= <span
class
=
"token punctuation"
>{
regExForName<span
class
=
"token punctuation"
>: <span
class
=
"token string"
>
""
<span
class
=
"token punctuation"
>,<span
class
=
"token comment"
>
// 定义名字的正则验证
regExForPhone<span
class
=
"token punctuation"
>: <span
class
=
"token string"
>
""
<span
class
=
"token punctuation"
>,<span
class
=
"token comment"
>
// 定义电话的正则验证
validateName<span
class
=
"token punctuation"
>: <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(name<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{
<span
class
=
"token comment"
>
// 对名字name做些操作，你可以通过使用“this.regExForname”
<span
class
=
"token comment"
>
// 访问regExForName变量
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>,
validatePhoneNo<span
class
=
"token punctuation"
>: <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(phoneNo<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{
<span
class
=
"token comment"
>
// 对电话号码做操作
<span
class
=
"token punctuation"
>}
<span
class
=
"token punctuation"
>}
<span
class
=
"token comment"
>
// 对象和方法一起申明
MYAPP<span
class
=
"token punctuation"
>.event <span
class
=
"token operator"
>= <span
class
=
"token punctuation"
>{
addListener<span
class
=
"token punctuation"
>: <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(el<span
class
=
"token punctuation"
>, type<span
class
=
"token punctuation"
>, fn<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token comment"
>
// 代码
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>,
removeListener<span
class
=
"token punctuation"
>: <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(el<span
class
=
"token punctuation"
>, type<span
class
=
"token punctuation"
>, fn<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token comment"
>
// 代码
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>,
getEvent<span
class
=
"token punctuation"
>: <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(e<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token comment"
>
// 代码
<span
class
=
"token punctuation"
>}
<span
class
=
"token comment"
>
// 还可以添加其他的属性和方法
<span
class
=
"token punctuation"
>}
<span
class
=
"token comment"
>
//使用addListner方法的写法:
MYAPP<span
class
=
"token punctuation"
>.event<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>addListener<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"yourel"
<span
class
=
"token punctuation"
>, <span
class
=
"token string"
>
"type"
<span
class
=
"token punctuation"
>, callback<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
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标准内置对象
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对象使用其随机（）方法来获得一个随机数。
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1
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<code
class
=
" language-js"
>console<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>log<span
class
=
"token punctuation"
>(Math<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>random<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></span></span></span></code>
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注意：T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。
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<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{ <span
class
=
"token punctuation"
>} <span
class
=
"token comment"
>
// 或
<span
class
=
"token keyword"
>
var
Person <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{ <span
class
=
"token punctuation"
>}</span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
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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).
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<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{ <span
class
=
"token punctuation"
>}
<span
class
=
"token keyword"
>
var
person1 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person2 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
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有两种为对象创建实例，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。
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<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
'Person instantiated'
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}
<span
class
=
"token keyword"
>
var
person1 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person2 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
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。
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<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(firstName<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName <span
class
=
"token operator"
>= firstName<span
class
=
"token punctuation"
>;
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
'Person instantiated'
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}
<span
class
=
"token keyword"
>
var
person1 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
'Alice'
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person2 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
'Bob'
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// Show the firstName properties of the objects
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
'person1 is '
<span
class
=
"token operator"
>+ person1<span
class
=
"token punctuation"
>.firstName<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// alerts "person1 is Alice"
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
'person2 is '
<span
class
=
"token operator"
>+ person2<span
class
=
"token punctuation"
>.firstName<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// alerts "person2 is Bob"</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
方法
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.
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<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(firstName<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName <span
class
=
"token operator"
>= firstName<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}
Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.sayHello <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Hello, I'm "
<span
class
=
"token operator"
>+ <span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person1 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Alice"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person2 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Bob"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// call the Person sayHello method.
person1<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>sayHello<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// alerts "Hello, I'm Alice"
person2<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>sayHello<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// alerts "Hello, I'm Bob"</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
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:
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<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(firstName<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName <span
class
=
"token operator"
>= firstName<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}
Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.sayHello <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Hello, I'm "
<span
class
=
"token operator"
>+ <span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person1 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Alice"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
person2 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Bob"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
var
helloFunction <span
class
=
"token operator"
>= person1<span
class
=
"token punctuation"
>.sayHello<span
class
=
"token punctuation"
>;
person1<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>sayHello<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// alerts "Hello, I'm Alice"
person2<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>sayHello<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// alerts "Hello, I'm Bob"
<span
class
=
"token function"
>helloFunction<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// alerts "Hello, I'm undefined" (or fails
<span
class
=
"token comment"
>
// with a TypeError in strict mode)
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(helloFunction <span
class
=
"token operator"
>=== person1<span
class
=
"token punctuation"
>.sayHello<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// alerts true
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(helloFunction <span
class
=
"token operator"
>=== Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.sayHello<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// alerts true
helloFunction<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>call<span
class
=
"token punctuation"
>(person1<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// alerts "Hello, I'm Alice"</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
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.
|
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|
<code
class
=
" language-js"
><span
class
=
"token comment"
>
// 定义Person构造器
<span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Person<span
class
=
"token punctuation"
>(firstName<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName <span
class
=
"token operator"
>= firstName<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}
<span
class
=
"token comment"
>
// 在Person.prototype中加入方法
Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.walk <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"I am walking!"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.sayHello <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Hello, I'm "
<span
class
=
"token operator"
>+ <span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// 定义Student构造器
<span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>Student<span
class
=
"token punctuation"
>(firstName<span
class
=
"token punctuation"
>, subject<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token comment"
>
// 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<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>call<span
class
=
"token punctuation"
>(<span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>, firstName<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// 初始化Student类特有属性
<span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.subject <span
class
=
"token operator"
>= subject<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// 建立一个由Person.prototype继承而来的Student.prototype对象.
<span
class
=
"token comment"
>
// 注意: 常见的错误是使用 "new Person()"来建立Student.prototype.
<span
class
=
"token comment"
>
// 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
<span
class
=
"token comment"
>
// 不能赋予Person类任何的FirstName参数
<span
class
=
"token comment"
>
// 调用Person的正确位置如下，我们从Student中来调用它
Student<span
class
=
"token punctuation"
>.prototype <span
class
=
"token operator"
>= Object<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>create<span
class
=
"token punctuation"
>(Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// See note below
<span
class
=
"token comment"
>
// 设置"constructor" 属性指向Student
Student<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.constructor <span
class
=
"token operator"
>= Student<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// 更换"sayHello" 方法
Student<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.sayHello <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Hello, I'm "
<span
class
=
"token operator"
>+ <span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.firstName <span
class
=
"token operator"
>+ <span
class
=
"token string"
>
". I'm studying "
<span
class
=
"token operator"
>+ <span
class
=
"token keyword"
>
this
<span
class
=
"token punctuation"
>.subject <span
class
=
"token operator"
>+ <span
class
=
"token string"
>
"."
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// 加入"sayGoodBye" 方法
Student<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>.sayGoodBye <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Goodbye!"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token comment"
>
// 测试实例:
<span
class
=
"token keyword"
>
var
student1 <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>Student<span
class
=
"token punctuation"
>(<span
class
=
"token string"
>
"Janet"
<span
class
=
"token punctuation"
>, <span
class
=
"token string"
>
"Applied Physics"
<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
student1<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>sayHello<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// "Hello, I'm Janet. I'm studying Applied Physics."
student1<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>walk<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// "I am walking!"
student1<span
class
=
"token punctuation"
>.<span
class
=
"token function"
>sayGoodBye<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// "Goodbye!"
<span
class
=
"token comment"
>
// Check that instanceof works correctly
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(student1 <span
class
=
"token keyword"
>
instanceof
<span
class
=
"token class-name"
>Person<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// true
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>(student1 <span
class
=
"token keyword"
>
instanceof
<span
class
=
"token class-name"
>Student<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// true</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
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：
|
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2
3
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5
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7
8
|
<code
class
=
" language-js"
><span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>createObject<span
class
=
"token punctuation"
>(proto<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{
<span
class
=
"token keyword"
>
function
<span
class
=
"token function"
>ctor<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>{ <span
class
=
"token punctuation"
>}
ctor<span
class
=
"token punctuation"
>.prototype <span
class
=
"token operator"
>= proto<span
class
=
"token punctuation"
>;
<span
class
=
"token keyword"
>
return
<span
class
=
"token keyword"
>
new
<span
class
=
"token class-name"
>ctor<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;
<span
class
=
"token punctuation"
>}
<span
class
=
"token comment"
>
// Usage:
Student<span
class
=
"token punctuation"
>.prototype <span
class
=
"token operator"
>= <span
class
=
"token function"
>createObject<span
class
=
"token punctuation"
>(Person<span
class
=
"token punctuation"
>.prototype<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
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）。
|
1
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3
|
<code
class
=
" language-js"
><span
class
=
"token keyword"
>
var
foo <span
class
=
"token operator"
>= <span
class
=
"token keyword"
>
function
<span
class
=
"token punctuation"
>(<span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>{<span
class
=
"token punctuation"
>}<span
class
=
"token punctuation"
>;
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>( <span
class
=
"token string"
>
'foo is a Function: '
<span
class
=
"token operator"
>+ <span
class
=
"token punctuation"
>(foo <span
class
=
"token keyword"
>
instanceof
<span
class
=
"token class-name"
>Function<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>; <span
class
=
"token comment"
>
// alerts "foo is a Function: true"
<span
class
=
"token function"
>alert<span
class
=
"token punctuation"
>( <span
class
=
"token string"
>
'foo.prototype is an Object: '
<span
class
=
"token operator"
>+ <span
class
=
"token punctuation"
>(foo<span
class
=
"token punctuation"
>.prototype <span
class
=
"token keyword"
>
instanceof
<span
class
=
"token class-name"
>Object<span
class
=
"token punctuation"
>) <span
class
=
"token punctuation"
>)<span
class
=
"token punctuation"
>;<span
class
=
"token comment"
>
// alerts "foo.prototype is an Object: true"</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></code>
|
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）。
注意
本文中所展示的面向对象编程技术不是唯一的实现方式，在JavaScript中面向对象的实现是非常灵活的。
同样的，文中展示的技术没有使用任何语言hacks，它们也没有模仿其他语言的对象理论实现。
JavaScript中还有其他一些更加先进的面向对象技术，但这些都超出了本文的介绍范围。
文章出处：https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript
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本文转自张昺华-sky博客园博客，原文链接：http://www.cnblogs.com/sunshine-anycall/p/4414045.html
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