JavaScript类/对象可以有构造函数吗?它们是如何产生的?


当前回答

例如:http://jsfiddle.net/FZ5nC/

试试这个模板:

<script>
//============================================================
// Register Namespace
//------------------------------------------------------------
var Name = Name||{};
Name.Space = Name.Space||{};

//============================================================
// Constructor - MUST BE AT TOP OF FILE
//------------------------------------------------------------
Name.Space.ClassName = function Name_Space_ClassName(){}

//============================================================
// Member Functions & Variables
//------------------------------------------------------------
Name.Space.ClassName.prototype = {
  v1: null
 ,v2: null
 ,f1: function Name_Space_ClassName_f1(){}
}

//============================================================
// Static Variables
//------------------------------------------------------------
Name.Space.ClassName.staticVar = 0;

//============================================================
// Static Functions
//------------------------------------------------------------
Name.Space.ClassName.staticFunc = function Name_Space_ClassName_staticFunc(){
}
</script>

如果你定义一个静态类,你必须调整你的命名空间:

<script>
//============================================================
// Register Namespace
//------------------------------------------------------------
var Shape = Shape||{};
Shape.Rectangle = Shape.Rectangle||{};
// In previous example, Rectangle was defined in the constructor.
</script>

示例类:

<script>
//============================================================
// Register Namespace
//------------------------------------------------------------
var Shape = Shape||{};

//============================================================
// Constructor - MUST BE AT TOP OF FILE
//------------------------------------------------------------
Shape.Rectangle = function Shape_Rectangle(width, height, color){
    this.Width = width;
    this.Height = height;
    this.Color = color;
}

//============================================================
// Member Functions & Variables
//------------------------------------------------------------
Shape.Rectangle.prototype = {
  Width: null
 ,Height: null
 ,Color: null
 ,Draw: function Shape_Rectangle_Draw(canvasId, x, y){
    var canvas = document.getElementById(canvasId);
    var context = canvas.getContext("2d");
    context.fillStyle = this.Color;
    context.fillRect(x, y, this.Width, this.Height);
 }
}

//============================================================
// Static Variables
//------------------------------------------------------------
Shape.Rectangle.Sides = 4;

//============================================================
// Static Functions
//------------------------------------------------------------
Shape.Rectangle.CreateSmallBlue = function Shape_Rectangle_CreateSmallBlue(){
    return new Shape.Rectangle(5,8,'#0000ff');
}
Shape.Rectangle.CreateBigRed = function Shape_Rectangle_CreateBigRed(){
    return new Shape.Rectangle(50,25,'#ff0000');
}
</script>

示例实例化:

<canvas id="painting" width="500" height="500"></canvas>
<script>
alert("A rectangle has "+Shape.Rectangle.Sides+" sides.");

var r1 = new Shape.Rectangle(16, 12, "#aa22cc");
r1.Draw("painting",0, 20);

var r2 = Shape.Rectangle.CreateSmallBlue();
r2.Draw("painting", 0, 0);

Shape.Rectangle.CreateBigRed().Draw("painting", 10, 0);
</script>

注意函数定义为A.B = function A_B()。这是为了使您的脚本更容易调试。打开Chrome的Inspect Element面板,运行这个脚本,并展开调试回溯:

<script>
//============================================================
// Register Namespace
//------------------------------------------------------------
var Fail = Fail||{};

//============================================================
// Static Functions
//------------------------------------------------------------
Fail.Test = function Fail_Test(){
    A.Func.That.Does.Not.Exist();
}

Fail.Test();
</script>

其他回答

使用上面Nick的示例,您可以使用return语句作为对象定义中的最后一条语句为不带参数的对象创建构造函数。返回你的构造函数,如下所示,它将在你每次创建对象时运行__construct中的代码:

function Box()
{
   var __construct = function() {
       alert("Object Created.");
       this.color = 'green';
   }

  this.color = '';

   this.getColor = function() {
       return this.color;
   }

   __construct();
}

var b = new Box();

http://www.jsoops.net/对于Js中的oop非常好。提供私有、受保护、公共变量和函数,并具有继承特性。示例代码:

var ClassA = JsOops(function (pri, pro, pub)
{// pri = private, pro = protected, pub = public

    pri.className = "I am A ";

    this.init = function (var1)// constructor
    {
        pri.className += var1;
    }

    pub.getData = function ()
    {
        return "ClassA(Top=" + pro.getClassName() + ", This=" + pri.getClassName()
        + ", ID=" + pro.getClassId() + ")";
    }

    pri.getClassName = function () { return pri.className; }
    pro.getClassName = function () { return pri.className; }
    pro.getClassId = function () { return 1; }
});

var newA = new ClassA("Class");

//***Access public function
console.log(typeof (newA.getData));
// function
console.log(newA.getData());
// ClassA(Top=I am A Class, This=I am A Class, ID=1)

//***You can not access constructor, private and protected function
console.log(typeof (newA.init));            // undefined
console.log(typeof (newA.className));       // undefined
console.log(typeof (newA.pro));             // undefined
console.log(typeof (newA.getClassName));    // undefined

我发现这个教程非常有用。大多数jQuery插件都使用这种方法。

http://www.htmlgoodies.com/html5/tutorials/create-an-object-oriented-javascript-class-constructor.html#fbid=OVYAQL_TDpK

var Class = function(methods) {   
    var klass = function() {    
        this.initialize.apply(this, arguments);          
    };  

    for (var property in methods) { 
       klass.prototype[property] = methods[property];
    }

    if (!klass.prototype.initialize) klass.prototype.initialize = function(){};      

    return klass;    
};

现在,

var Person = Class({ 
    initialize: function(name, age) {
        this.name = name;
        this.age  = age;
    },
    toString: function() {
        return "My name is "+this.name+" and I am "+this.age+" years old.";
    }
}); 

var alice = new Person('Alice', 26);
alert(alice.name); //displays "Alice"
alert(alice.age); //displays "26"
alert(alice.toString()); //displays "My name is Alice and I am 26 years old" in most browsers.
//IE 8 and below display the Object's toString() instead! "[Object object]"

构造函数的意义是什么呢 财产吗?不知道它在哪里 可能有用,有什么想法吗?

构造函数属性的目的是提供某种方式来假装JavaScript有类。你不能做的一件事是在创建对象后更改对象的构造函数。它是复杂的。

几年前我写了一篇相当全面的文章:http://joost.zeekat.nl/constructors-considered-mildly-confusing.html

使用原型:

function Box(color) // Constructor
{
    this.color = color;
}

Box.prototype.getColor = function()
{
    return this.color;
};

隐藏“color”(有点像私有成员变量):

function Box(col)
{
   var color = col;

   this.getColor = function()
   {
       return color;
   };
}

用法:

var blueBox = new Box("blue");
alert(blueBox.getColor()); // will alert blue

var greenBox = new Box("green");
alert(greenBox.getColor()); // will alert green