JavaScript类/对象可以有构造函数吗?它们是如何产生的?
当前回答
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
其他回答
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>
我想我会发布我用javascript闭包做的事情,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。:)
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。
也许它变得简单了一点,但以下是我在2017年想出的:
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,我有以下:
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,我们设置对象的属性。我们还通过使用setter函数改变对象的颜色和形状,并证明在这些改变之后调用getInfo()时它的变化仍然存在。
有点晚了,但我希望这能帮到你。我已经用摩卡单元测试了这个功能,效果很好。
这是一个构造函数:
function MyClass() {}
当你这样做时
var myObj = new MyClass();
MyClass被执行,并返回该类的一个新对象。