I am doing something wrong with this prototype in JavaScript, any ideas?

The following code doesn't produce a prototype like I thought it might. Can anyone see what I am doing wrong?

var A = function () {
    return {
        workingTest: function () {return "OK";}
    };
}开发者_JS百科;

A.prototype.notWorkingTest = function () {return "Not so much";};

var a = new A();

a.workingTest(); // "OK"
a.notWorkingTest(); // TypeError: "undefined_method"

Any ideas? I thought that this was the right way to extend JS classes, but I am missing something.

---

Change A to

var A = function () {
  this.workingTest = function () {return "OK";};
};

The problem is that your original A function was creating and returning a direct instance of Object instead of using the instance of A that was created by the new operator and bound to this.

To understand this, try running

var B = function () { return { x: 42 }; }
var C = function () { this.x = 42; }
var b = new B;
var c = new C;
alert("b.constructor === B : " + (b.constructor === B));  // false
alert("b.constructor === Object : " + (b.constructor === Object));  // true
alert("c.constructor === C : " + (c.constructor === C));  // true

So because B returns a new object, the value it returns is no longer an instanceof B and does not use B's prototype.

---

Because A returns a separate object, a is not an instance of the A class; rather, it's an ordinary object which happens to be returned by the A function.
It is not connected to A or its prototype at all.

Instead, you need to assign workingTest to this inside the constructor and not return anything at all:

var A = function () {
    this.workingTest = function () { return "OK"; };
};

---

Because you extend A's prototype while the new A() returns an "anonymous" object.

---

In a modern browser, you can keep your interesting prototyping approach with:

var A = {
  workingTest: function () {return "OK";}
};
A.notWorkingTest = function () {return "Yes it does";};

var a = Object.create (A);
a.workingTest(); // "OK"
a.notWorkingTest(); // "Yes it does"

a.extending = function () {return "extended";};
var b = Object.create(a);
b.workingTest(); // "OK"
b.extending();  // "extended"

This works according to the ES5 spec.

---

You defined A as a function that returns an object literal. Using the new keyword when calling a function implies that it is a special type of function, namely a constructor. Constructors in JavaScript must be written in a specific way, setting properties using the this keyword.

var A = function () {
  this.workingTest = function () {return "OK";};
};