javascript对象中的构造函数

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;
   };
}

用途:

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

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

这是一个我在javascript中用于OOP类似行为的模板。如您所见,您可以使用闭包模拟私有(静态和实例)成员。什么 new MyClass() will-return是一个对象,只分配给 this 对象和中的 prototype “类”的对象。

var MyClass = (function () {
    // private static
    var nextId = 1;

    // constructor
    var cls = function () {
        // private
        var id = nextId++;
        var name = 'Unknown';

        // public (this instance only)
        this.get_id = function () { return id; };

        this.get_name = function () { return name; };
        this.set_name = function (value) {
            if (typeof value != 'string')
                throw 'Name must be a string';
            if (value.length < 2 || value.length > 20)
                throw 'Name must be 2-20 characters long.';
            name = value;
        };
    };

    // public static
    cls.get_nextId = function () {
        return nextId;
    };

    // public (shared across instances)
    cls.prototype = {
        announce: function () {
            alert('Hi there! My id is ' + this.get_id() + ' and my name is "' + this.get_name() + '"!\r\n' +
                  'The next fellow\'s id will be ' + MyClass.get_nextId() + '!');
        }
    };

    return cls;
})();

我被问到使用这个模式继承的问题,下面是:

// It's a good idea to have a utility class to wire up inheritance.
function inherit(cls, superCls) {
    // We use an intermediary empty constructor to create an
    // inheritance chain, because using the super class' constructor
    // might have side effects.
    var construct = function () {};
    construct.prototype = superCls.prototype;
    cls.prototype = new construct;
    cls.prototype.constructor = cls;
    cls.super = superCls;
}

var MyChildClass = (function () {
    // constructor
    var cls = function (surName) {
        // Call super constructor on this instance (any arguments
        // to the constructor would go after "this" in call(…)).
        this.constructor.super.call(this);

        // Shadowing instance properties is a little bit less
        // intuitive, but can be done:
        var getName = this.get_name;

        // public (this instance only)
        this.get_name = function () {
            return getName.call(this) + ' ' + surName;
        };
    };
    inherit(cls, MyClass); // <-- important!

    return cls;
})();

以及一个使用它的例子:

var bob = new MyClass();
bob.set_name('Bob');
bob.announce(); // id is 1, name shows as "Bob"

var john = new MyChildClass('Doe');
john.set_name('John');
john.announce(); // id is 2, name shows as "John Doe"

alert(john instanceof MyClass); // true

如您所见,这些类彼此正确地交互(它们共享来自 MyClass , the announce 方法使用正确的 get_name 方法等)

需要注意的一点是需要隐藏实例属性。你真的可以 inherit 函数遍历所有实例属性(使用 hasOwnProperty )这是函数,并自动添加 super_<method name> 财产。这样你就可以打电话了 this.super_get_name() 而不是将其存储在临时值中并使用 call .

对于原型上的方法,您不需要担心上面的问题,但是,如果您想要访问超级类的原型方法,您可以调用 this.constructor.super.prototype.methodName . 如果您想让它不那么冗长,当然可以添加便利属性。:)

在我看来,你们大多数人都在举getter和setter的例子,而不是构造函数。 http://en.wikipedia.org/wiki/Constructor_(object-oriented_programming) .

吃过午饭的丹离我们更近了,但这个例子在jsiddle中不起作用。

这个例子创建了一个只在对象创建期间运行的私有构造函数函数。

var color = 'black';

function Box()
{
   // private property
   var color = '';

   // private constructor 
   var __construct = function() {
       alert("Object Created.");
       color = 'green';
   }()

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

   // setter
   this.setColor = function(data) {
       color = data;
   }

}

var b = new Box();

alert(b.getColor()); // should be green

b.setColor('orange');

alert(b.getColor()); // should be orange

alert(color); // should be black

如果要分配公共属性,则可以将构造函数定义为:

var color = 'black';

function Box()
{
   // public property
   this.color = '';

   // private constructor 
   var __construct = function(that) {
       alert("Object Created.");
       that.color = 'green';
   }(this)

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

   // setter
   this.setColor = function(color) {
       this.color = color;
   }

}

var b = new Box();

alert(b.getColor()); // should be green

b.setColor('orange'); 

alert(b.getColor()); // should be orange

alert(color); // should be black

那么“构造函数”的意义何在? 财产?不知道它在哪里 可能有用,有什么想法吗?

构造器属性的要点是提供一些假装javascript具有类的方法。其中一件事就是你 不能 有效的做法是在创建对象后更改其构造函数。这很复杂。

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

例子如下: http://jsfiddle.net/FZ5nC/

尝试此模板:

<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>

如果要定义静态类,则必须调整命名空间:

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

实例类:

<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>

注意函数被定义为a.b=函数a_b()。这是为了使脚本更容易调试。打开chrome的inspect element面板,运行此脚本,然后展开debug backtrace:

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

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

Fail.Test();
</script>

这是一个构造函数:

function MyClass() {}

当你这样做的时候

var myObj = new MyClass();

MyClass 执行,并返回该类的新对象。

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]"

这种模式对我很有帮助。使用这种模式,您可以在单独的文件中创建类,并根据需要将它们加载到整个应用程序中。

// Namespace
// (Creating new if not instantiated yet, otherwise, use existing and just add to it)
var myApp = myApp || {};

// "Package" 
// Similar to how you would establish a package in other languages
(function() {

// "Class"
var MyClass = function(params) {
    this.initialize(params);
}

    // "Private Static" vars 
    //    - Only accessible to functions in this class.
    //    - Doesn't get wiped out when we create a new instance.
    var countInstances = 0;
    var allInstances = [];

    // "Private Static" functions 
    //    - Same as above, but it's a function accessible 
    //      only to other functions in this class.
    function doSomething(){
    }

    // "Public Static" vars
    //    - Everyone has access.
    //    - Doesn't get wiped out when we create a new instance.
    MyClass.counter = 0;

    // "Public Static" functions
    //    - Same as above, but anyone can call this "static method".
    //    - Kinda like a singleton class situation.
    MyClass.foobar = function(){
    }

    // Public properties and methods are built into the "prototype"
    //    - This is how each instance can become unique unto itself.
    //    - Establishing "p" as "local" (Static Private) variable 
    //      simply so we don't have to keep typing "MyClass.prototype" 
    //      for each property and function.
var p = MyClass.prototype;

    // "Public" vars
    p.id = null;
    p.firstname = null;
    p.lastname = null;

    // "Private" vars
    //    - Only used by "this" instance.
    //    - There isn't "true" privacy for each 
    //      instance so we have to fake it. 
    //    - By tradition, we indicate "privacy"  
    //      by prefixing it with an underscore. 
    //    - So technically, anyone can access, but we simply 
    //      don't tell anyone about it (e.g. in your API)
    //      so no one knows about it :)
    p._foo = null;

    p.initialize = function(params){
        this.id = MyClass.counter++;
        this.firstname = params.firstname;
        this.lastname = params.lastname;
        MyClass.counter++;
        countInstances++;
        allInstances.push(this);
    }

    p.doAlert = function(theMessage){
        alert(this.firstname + " " + this.lastname + " said: " + theMessage + ". My id:" + this.id + ".  Total People:" + countInstances + ". First Person:" + allInstances[0].firstname + " " + allInstances[0].lastname);
    }


// Assign class to app
myApp.MyClass = MyClass;

// Close the "Package"
}());

// Usage example:
var bob = new myApp.MyClass({   firstname   :   "bob",
                                lastname    :   "er"
                            });

bob.doAlert("hello there");

是的,可以这样定义类声明中的构造函数:

class Rectangle {
  constructor(height, width) {
    this.height = height;
    this.width = width;
  }
}

我想我会发布我对JavaScript闭包所做的,因为还没有人使用闭包。

var user = function(id) {
  // private properties & methods goes here.
  var someValue;
  function doSomething(data) {
    someValue = data;
  };

  // constructor goes here.
  if (!id) return null;

  // public properties & methods goes here.
  return {
    id: id,
    method: function(params) {
      doSomething(params);
    }
  };
};

欢迎对此解决方案提出意见和建议。:)

使用上面的尼克示例,可以为对象创建一个构造函数 没有 使用返回语句作为对象定义中的最后一条语句的参数。按如下所示返回构造函数函数,它将在每次创建对象时运行\构造中的代码:

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

  this.color = '';

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

   __construct();
}

var b = new Box();

如果你用的话 Typescript -从Microsoft打开源代码:-)

class BankAccount {
 balance: number;
 constructor(initially: number) {
 this.balance = initially;
 }
 deposit(credit: number) {
 this.balance += credit;
 return this.balance;
 }
}

typescript允许您“伪造”被编译成javascript构造的OO构造。如果您正在启动一个大型项目,它可能会节省您很多时间,并且它刚刚达到里程碑1.0版本。

http://www.typescriptlang.org/Content/TypeScript%20Language%20Specification.pdf

以上代码将“编译”为:

var BankAccount = (function () {
    function BankAccount(initially) {
        this.balance = initially;
    }
    BankAccount.prototype.deposit = function (credit) {
        this.balance += credit;
        return this.balance;
    };
    return BankAccount;
})();

也许会简单一点,但下面是我在2017年提出的建议:

class obj {
  constructor(in_shape, in_color){
    this.shape = in_shape;
    this.color = in_color;
  }

  getInfo(){
    return this.shape + ' and ' + this.color;
  }
  setShape(in_shape){
    this.shape = in_shape;
  }
  setColor(in_color){
    this.color = in_color;
  }
}

在使用上面的类时,我有以下内容:

var newobj = new obj('square', 'blue');

//Here, we expect to see 'square and blue'
console.log(newobj.getInfo()); 

newobj.setColor('white');
newobj.setShape('sphere');

//Since we've set new color and shape, we expect the following: 'sphere and white'
console.log(newobj.getInfo());

如您所见,构造函数接受两个参数,我们设置了对象的属性。我们还通过使用 setter 函数,并证明其在调用时仍保持更改 getInfo() 在这些变化之后。

有点晚了,但我希望这有帮助。我用一个 mocha 单元测试,而且工作正常。

在javascript中,调用类型定义函数的行为:

• 直接调用 func()
• 对象上的方法调用 obj.func()
• 构造函数 调用 new func()
• 间接调用 func.call() 或 func.apply()

函数作为 构造函数 调用时使用 new 操作员:

function Cat(name) {
   this.name = name;
}
Cat.prototype.getName = function() {
   return this.name;
}

var myCat = new Cat('Sweet'); // Cat function invoked as a constructor

javascript中的任何实例或原型对象都有一个属性 constructor ,表示构造函数函数。

Cat.prototype.constructor === Cat // => true
myCat.constructor         === Cat // => true

检查 this post 关于构造函数属性。

当从上面使用Blixt的伟大模板时,我发现它在多层继承(MyGrandChildClass扩展MyChildClass扩展MyClass)中不能很好地工作,它反复调用第一个父类的构造函数。因此,如果您需要多层次继承,而不是使用 this.constructor.super.call(this, surName); 使用 chainSuper(this).call(this, surName); 链函数的定义如下:

function chainSuper(cls) {
  if (cls.__depth == undefined) cls.__depth = 1; else cls.__depth++;
  var depth = cls.__depth;
  var sup = cls.constructor.super;
  while (depth > 1) {
    if (sup.super != undefined) sup = sup.super;
    depth--;
  }
  return sup;
}

http://www.jsoops.net/ 在JS中非常适合OOP。如果提供private、protected、public变量和函数,以及继承功能。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

只是提供一些多样性。 ds.oop 是用JavaScript中的构造函数声明类的好方法。它支持所有可能的继承类型(包括1个甚至C都不支持的类型)以及很好的接口。

var Color = ds.make.class({
    type: 'Color',
    constructor: function (r,g,b) { 
        this.r = r;                     /* now r,g, and b are available to   */
        this.g = g;                     /* other methods in the Color class  */
        this.b = b;                     
    }
});
var red = new Color(255,0,0);   // using the new keyword to instantiate the class

这里我们需要注意Java脚本中的一个点,它是一个无类语言,但是,我们可以通过使用Java脚本中的函数来实现它。最常见的实现方法是,我们需要在Java脚本中创建一个函数并使用 新的 关键字 创建对象并使用 这 关键字 定义属性和方法。下面是示例。

// Function constructor

   var calculator=function(num1 ,num2){
   this.name="This is function constructor";
   this.mulFunc=function(){
      return num1*num2
   };

};

var objCal=new calculator(10,10);// This is a constructor in java script
alert(objCal.mulFunc());// method call
alert(objCal.name);// property call

//Constructors With Prototypes

var calculator=function(){
   this.name="Constructors With Prototypes";
};

calculator.prototype.mulFunc=function(num1 ,num2){
 return num1*num2;
};
var objCal=new calculator();// This is a constructor in java script
alert(objCal.mulFunc(10,10));// method call
alert(objCal.name); // property call

在大多数情况下,在调用传递此信息的方法之前,必须以某种方式声明所需的属性。如果最初不需要设置属性,可以这样在对象内调用方法。也许这不是最漂亮的方法,但这仍然有效。

var objectA = {
    color: ''; 
    callColor : function(){
        console.log(this.color);
    }
    this.callColor(); 
}
var newObject = new objectA();