JavaScript类/对象可以有构造函数吗?它们是如何产生的?
当前回答
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
其他回答
如果你使用微软开源的Typescript,他们就会这样做:-)
class BankAccount {
balance: number;
constructor(initially: number) {
this.balance = initially;
}
deposit(credit: number) {
this.balance += credit;
return this.balance;
}
}
Typescript让你“伪造”OO结构,这些结构被编译成javascript结构。如果你正在开始一个大型项目,它可以为你节省很多时间,而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;
})();
在JavaScript中调用类型定义了函数的行为:
直接调用 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()
该函数在使用new操作符调用时作为构造函数调用:
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构造函数,它引用构造函数。
Cat.prototype.constructor === Cat // => true
myCat.constructor === Cat // => true
查看这篇关于构造函数属性的文章。
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();
在我看来,你们大多数人都给出了getter和setter的例子,而不是一个构造函数,即http://en.wikipedia.org/wiki/Constructor_(object-oriented_programming)。
lunch -dan更接近,但是这个例子在jsFiddle中不起作用。
这个例子创建了一个私有构造函数,该函数只在创建对象期间运行。
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
如果你想要分配公共属性,那么构造函数可以这样定义:
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
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>