如何使用构造函数方法创建一个javascript类来启动新对象/实例？

Question

I'm experimenting with javascript. I'm trying to make a "class" but it is not working like it should. I have problems initiating a new instance of MyClass. See the js fiddle. Is it possible to add a constructor to MyClass just like in php? I'm also not sure that this is the way "classes" are defined in javascript. So any help is more then appreciated.

http://jsfiddle.net/kasperfish/JnvFS/

    var MyClass={
        test:'hello',

        hallo: function(){
            alert(this.test);
        },

        setTest: function(x){
            this.test=x;
        }

    }

MyClass.hallo();
MyClass.setTest('world');
MyClass.hallo();

//not working because MyClass is/does not have a constructor
x= new MyClass;//*
x.hallo(); 

* firebug: TypeError: MyClass is not a constructor

Answer 1

In JavaScript, the constructor of a class is just a function, and the members are set either in there, or using the prototype object. For example:

function MyClass(someArgument) {
   // construction, init members of this
   this.someField = someArgument;
   this.test = 'a test';
}

// in addition, all members of `prototype` are automatically set on every 
// new instance of MyClass.
MyClass.prototype.hallo = function(){
         alert(this.test);
};

and then

var inst = new MyClass(42);
inst.hallo();

I suggest you read up on prototype-based OOP in JavaScript. It is definitely different than the one you may be used to from PHP, and it generally does not feel very intuitive.

Answer 2

You're gonna have to make your MyClass Object a function like this:

var MyClass = function() {
    this.test = 'Hello';
};

MyClass.prototype.hello = function() {
    alert(this.test);
};

MyClass.prototype.setTest = function( x ) {
    this.test = x;
};

var myInstance = new MyClass();

myInstance.hello();
myInstance.setTest('World');
myInstance.hello();

Answer 3

ok, firstly you should know that javascript does not have "classes" per say, javascript datastructures are indeed made of objects but as you can see from your code above, objects are essentially key-value pairs much unlike other languages like php, the implementation of OOP in javascript is very different.

if you would like to use a constructor to create instances of your object, then try and create your "class" using a function, a construtor, maybe in this way:

function MyClass(){
    this.test ='hello';
    this.hallo = function(){
                     alert(this.test);
                 };

    this.setTest = function(x){
                       this.test=x;
                   };
}

var myClassInstance = new MyClass();
myClassInstance.hallo();
myClassInstance.setTest('world');
myClassInstance.hallo();

i hope this helps