JavaScript类/对象可以有构造函数吗?它们是如何产生的?
当前回答
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。:)
其他回答
这种模式对我很有帮助。使用这种模式,你在单独的文件中创建类,“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");
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
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。如果你不需要一开始就设置一个属性,你可以像这样在对象中调用一个方法。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();