How do we create instances of a class in JavaScript using new operator and factory pattern?

Question

I am trying to make a class (called Foo) like object in JavaScript that would let me create multiple instances of Foo. By multiple instances, I mean, each instance would maintain separate internal state. This is how I am achieving it.

var Foo = function() {
    function init(a) {
        this.a = a
    }

    function state() {
        return this.a
    }

    function getFoo() {
        return {
            init: init,
            state: state
        }
    }

    return {
        getFoo: getFoo
    }
}()

var a = Foo.getFoo()
var b = Foo.getFoo()
a.init(10)
b.init(20)
alert(a.state() + ', ' + b.state())

As you can see that the Foo.getFoo() seems to simulate the Factory pattern usually used in Java. The internal state is the variable this.a. I consider my attempt a success because a.state() and b.state() display two different internal states. However, this is purely my attempt without any knowledge of how these things are implemented in the industry.

Now, my questions may seem like a request for code review and is at the risk of getting closed, so I will try to make my questions as objective as possible.

How can the same code be implemented such that new operator can be used instead to create the new instances of a class with this.a as the internal state?
How is my code with the factory pattern written in the industry?

Check out this excellent resource.

MD Sayem Ahmed
– MD Sayem Ahmed

2013-08-22 06:03:58 +00:00
Commented Aug 22, 2013 at 6:03 — MD Sayem Ahmed
– MD Sayem Ahmed, Commented Aug 22, 2013 at 6:03

Vladislav Qulin · Accepted Answer · 2013-08-22 06:32:16Z

3

var Foo = function (a) {
    this.a = a;
};
Foo.prototype.state = function () {
    return this.a;
};

var a = new Foo(10);
a.state(); // 10

Bun you can also declare the state method from constructor itself like:

var Foo = function (a) {
    this.a = a;
    this.state = function () {
        return this.a;
    };
};

UPDATE: Factory pattern.

I usually use this for my factories:

var Foo = function (a) {
    this.a = a;
};
Foo.prototype.state = function () {
    return this.a;
};

var FooFactory = function () {};
FooFactory.prototype.create = function (a) {
    return new Foo(a);
};

var factory = new FooFactory();
var a = factory.create(20);
a instanceOf Foo; // true
a.state(); // 20

edited Aug 22, 2013 at 6:32

answered Aug 22, 2013 at 6:02

Vladislav Qulin

1,9321 gold badge17 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

Vladislav Qulin Over a year ago

It doesn't help you, does it?

Bart Over a year ago

Don't say that :) This is exactly what I would do. The original code isn't really a producer of Foo. It just combines some functions to make it resemble Foo. Also having the object not be the factory simplifies the code.

Lone Learner Over a year ago

@VladislavQulin It does help. I'll be accepting this answer in a couple of days once I wrap my mind around these concepts. :-)

kayz1 Over a year ago

var FooFactory = function () {}; FooFactory.create = function (a) { return new Foo(a); }; var a = FooFactory.create(20);

Vladislav Qulin Over a year ago

I work with large project with whole lot of different classes, so i prefer factory pattern. But it could be professional deformation. One for sure, you should come from your needs and don't make premature optimization.

|

Collectives™ on Stack Overflow

How do we create instances of a class in JavaScript using new operator and factory pattern?

1 Answer 1

9 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

9 Comments

Your Answer

Sign up or log in

Post as a guest

Related