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A brief analysis of types and objects in JavaScript_javascript skills

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2016-05-16 17:11:49923browse

JavaScript是基于对象的,任何元素都可以看成对象。然而,类型和对象是不同的。本文中,我们除了讨论类型和对象的一些特点之外,更重要的是研究如何写出好的并且利于重用的类型。毕竟,JavaScript这种流行的脚本语言如果能够进行良好的封装,并形成一个庞大的类型库,对于重用是非常有意义的。

网上对于prototype的文章很多,一直没明白核心的思想。最后写了很多例子代码后才明白:prototype只能用在类型上。

以下是一些关于类型和对象的例子,大家看完例子后可能更容易理解类型和对象之间的联系:

 
例子代码
说明
1
Object.prototype.Property = 1;
Object.prototype.Method = function ()
{
    alert(1);
}
 
var obj = new Object();
alert(obj.Property);
obj.Method();
可以在类型上使用proptotype来为类型添加行为。这些行为只能在类型的实例上体现。

JS中允许的类型有Array, Boolean, Date, Enumerator, Error, Function, Number, Object, RegExp, String
2
var obj = new Object();
obj.prototype.Property = 1; //Error
//Error
obj.prototype.Method = function()
{
    alert(1);
}
在实例上不能使用prototype,否则发生编译错误
3
Object.Property = 1;
Object.Method = function()
{
    alert(1);
}
 
alert(Object.Property);
Object.Method();
可以为类型定义“静态”的属性和方法,直接在类型上调用即可
4
Object.Property = 1;
Object.Method = function()
{
    alert(1);
}
var obj = new Object();
alert(obj.Property); //Error
obj.Method(); //Error
实例不能调用类型的静态属性或方法,否则发生对象未定义的错误。
5
function Aclass()
{
this.Property = 1;
this.Method = function()
{
    alert(1);
}
}
var obj = new Aclass();
alert(obj.Property);
obj.Method();
这个例子演示了通常的在JavaScript中定义一个类型的方法
6
function Aclass()
{
this.Property = 1;
this.Method = function()
{
    alert(1);
}
}
Aclass.prototype.Property2 = 2;
Aclass.prototype.Method2 = function
{
    alert(2);
}
var obj = new Aclass();
alert(obj.Property2);
obj.Method2();
可以在外部使用prototype为自定义的类型添加属性和方法。
7
function Aclass()
{
this.Property = 1;
this.Method = function()
{
    alert(1);
}
}
Aclass.prototype.Property = 2;
Aclass.prototype.Method = function
{
    alert(2);
}
var obj = new Aclass();
alert(obj.Property);
obj.Method();
在外部不能通过prototype改变自定义类型的属性或方法。
该例子可以看到:调用的属性和方法仍是最初定义的结果。
8
function Aclass()
{
this.Property = 1;
this.Method = function()
{
    alert(1);
}
}
var obj = new Aclass();
obj.Property = 2;
obj.Method = function()
{
    alert(2);
}
alert(obj.Property);
obj.Method();
可以在对象上改变属性。(这个是肯定的)
也可以在对象上改变方法。(和普遍的面向对象的概念不同)
9
function Aclass()
{
this.Property = 1;
this.Method = function()
{
    alert(1);
}
}
var obj = new Aclass();
obj.Property2 = 2;
obj.Method2 = function()
{
    alert(2);
}
alert(obj.Property2);
obj.Method2();
可以在对象上增加属性或方法
10
function AClass()
{
       this.Property = 1;
       this.Method = function()
       {
              alert(1);
       }
}
 
function AClass2()
{
       this.Property2 = 2;
       this.Method2 = function()
       {
              alert(2);
       }
}
AClass2.prototype = new AClass();
 
var obj = new AClass2();
alert(obj.Property);
obj.Method();
alert(obj.Property2);
obj.Method2();
This example illustrates how one type inherits from another type.
11
function AClass()
{
this.Property = 1;
this.Method = function()
{
alert(1);
}
}
function AClass2()
{
this.Property2 = 2;
this.Method2 = function()
{
alert(2);
}
}
AClass2.prototype = new AClass();
AClass2.prototype.Property = 3;
AClass2.prototype.Method = function()
{
alert(4);
}
var obj = new AClass2();
alert(obj.Property);
obj.Method();
This example illustrates how a subclass can override the properties or methods of a parent class.
In the above example, the important aspects of reuse through types are:
·Example 1: Types that allow adding behaviors in JavaScript
·Example 2 : Restrictions on the use of prototype
·Example 3: How to define static members of a type
·Example 7: Restrictions of prototype on redefining members of a type
·Example 10: How to make one type inherit from another A type
·Example 11: How to redefine members of the parent class in a subclass

The object-oriented features that JavaScript can implement are:
·Public field
·Public Method
·Private field
·Private method (private field)
·Method overload
·Constructor
·Event
·Single inherit
·Subclass overrides the properties or methods of the parent class (override)
·Static properties or Method(static member)
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