JavaScript对象中的构造方法

JavaScript类/对象可以具有构造函数吗？ 它们是如何创建的？

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#1楼

这是一个构造函数：

function MyClass() {}

当你做

var myObj = new MyClass();

执行MyClass ，并返回该类的新对象。

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#2楼

我想我会发布有关javascript闭包的信息，因为目前还没有人使用闭包。

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。 :)

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#3楼

这是我有时在JavaScript中用于OOP相似行为的模板。 如您所见，您可以使用闭包来模拟私有（静态和实例）成员。 new MyClass()将返回的对象是仅具有分配给this对象的属性，并且位于“类”的prototype对象中。

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;
})();

有人问我使用这种模式的继承，所以去了：

// 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;
})();

并使用所有示例：

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，这些类之间可以正确交互（它们共享MyClass的静态ID， announce方法使用正确的get_name方法，等等）。

需要注意的一件事是需要对实例属性进行阴影处理。 实际上，您可以使inherit函数遍历作为函数的所有实例属性（使用hasOwnProperty ），并自动添加super_<method name>属性。 这样您就可以调用this.super_get_name()而不是将其存储在一个临时值中并使用call对其进行绑定。

对于原型上的方法，您无需担心上述问题，如果您要访问超类的原型方法，则可以调用this.constructor.super.prototype.methodName 。 如果您想使其更简洁一些，您当然可以添加便捷属性。 :)

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#4楼

使用原型：

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

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

隐藏“颜色”（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

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#5楼

在我看来，你们中的大多数人都在提供getter和setter的示例而不是构造函数，即http://en.wikipedia.org/wiki/Constructor_(object-oriented_programming） 。

Lunched-dan更近了，但是该示例在jsFiddle中不起作用。

本示例创建一个私有构造函数，该函数仅在对象创建期间运行。

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，则可以按以下方式定义构造函数：

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

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#6楼

这种模式对我很好。 使用这种模式，您可以在单独的文件中创建类，然后“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");

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#7楼

我发现本教程非常有用。 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]"

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#8楼

此处的示例： 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>

如果要定义静态类，则必须调整名称空间：

<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：

<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AB =函数A_B（）。 这是为了使脚本更易于调试。 打开Chrome的Inspect Element面板，运行此脚本，然后展开调试回溯：

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

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

Fail.Test();
</script>

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#9楼

从上面使用Blixt的出色模板时，我发现它不能与多级继承（MyGrandChildClass扩展MyChildClass扩展MyClass）配合使用-反复调用第一个父级的构造函数。 因此，这是一个简单的解决方法–如果您需要多级继承，而不是使用this.constructor.super.call(this, surName); 使用chainSuper(this).call(this, surName); 链函数定义如下：

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;
}

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#10楼

如果您使用Typescript，它们会执行-MicroSoft开放源代码：-)

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

Typescript可让您“伪造”已编译为javascript构造的OO构造。 如果您正在启动一个大型项目，则可能会节省大量时间，并且它刚刚达到里程碑1.0版本。

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

上面的代码被“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;
})();

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#11楼

http://www.jsoops.net/对于Js中的oop非常有用。 如果提供私有，受保护的公共变量和函数，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

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#12楼

只是为了提供一些变化。 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（包括甚至c＃不支持的1种继承）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

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#13楼

在大多数情况下，您必须以某种方式声明所需的属性，然后才能调用传递此信息的方法。 如果您不必最初设置属性，则可以像这样在对象内调用方法。 可能不是最漂亮的方法，但这仍然有效。

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

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#14楼

在JavaScript中，调用类型定义了函数的行为：

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

---

使用new运算符进行调用时，该函数作为构造函数被调用：

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 ，它是指构造函数。

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

检查这个职位约constructor属性。

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#15楼

是的，您可以在类声明中定义一个构造函数，如下所示：

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

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#16楼

也许它变得更简单了，但是下面是我现在在2017年提出的内容：

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，然后我们设置对象的属性。 我们还使用setter函数更改了对象的颜色和形状，并证明在这些更改后调用getInfo()保留其更改。

有点晚了，但是我希望这会有所帮助。 我已经通过mocha单元测试对此进行了测试，并且运行良好。

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#17楼

这里我们需要注意Java脚本中的一点，它是一种无类语言，但是我们可以通过使用Java脚本中的函数来实现。 实现此目的的最常见方法是，需要在Java脚本中创建一个函数，并使用new 关键字创建一个对象，然后使用此 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

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#18楼

那么“构造函数”属性的意义是什么？ 无法找出在哪里有用的任何想法？

构造器属性的重点是提供一种伪装JavaScript has classes的方法。 您无法做的一件事是在创建对象后更改对象的构造函数。 情况很复杂。

几年前，我在上面写了一篇相当全面的文章： http : //joost.zeekat.nl/constructors-considered-mildly-confusing.html

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#19楼

使用上面的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。 返回如下所示的构造函数，每次创建对象时，它将在__construct中运行代码：

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

  this.color = '';

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

   __construct();
}

var b = new Box();

来源：CSDN

作者：asdfgh0077

链接：https://blog.csdn.net/asdfgh0077/article/details/104196083