Empty Function use in Javascript

Question

I am trying to understand a third party Javascript code. But am not able to figure out what is the use of the below coding style.

 function A(){
    }
A.Prop = '23';
A.generate = function(n){
   // do something
}

And then it is just used as :

A.generate(name);

Can someone explain what this code is doing. I understand some bit of OO Javascript, but i wonder if this is any other form of extending an object with new properties to it. Though i dont see any "new" keyword being used, to create an object.

Any ideas ?

Thanks,

Solution 1

They are creating a namespace. There are many ways to do this, and all are more-or-less equivalent:

A = {
    Prop : '23',
    generate : function (n) {
        // do something
    }
};

Or, equivalently:

A = { };
A.Prop = '23';
A.generate = function (n) {
    // do something
};

Also, if you like being verbose:

A = new Object();
A.Prop = '23';
A.generate = function (n) {
    // do something
};

function is usually used to denote a "class" rather than a "namespace", like so:

A = (function () {
    var propValue = '23';    // class local variable
    return {
        "Prop" : propValue,
        "generate" : function (n) {
            // do something
        }
    };
})();
// then I can use A in the same way as before:
A.generate(name);

Solution 2

It looks like they're using a dummy function to create a namespace.

You're right; this is useless.
They should use a normal object instead.

Comments

[duskandawn]

Thanks, for the answer, i was thinking on the same lines. But do you know will there be any performance issue, using this coding style. I mean to say is this a general way to create namespaces. I would assume code var A = new function(){}(); code to do something like this, if i dont touch the whole codebase ?

[SLaks]

The correct way to create a namespace is to use an object literal: var a = { };.

[Andrew]

Unless they want to support "instances" of that object, right? function A(){} allows for the var a = new A(); pattern, I think.

[SLaks]

@Andrew: But they're not making a class.

[Andrew]

@SLaks, what specifically makes you sure of that?

[SLaks]

@Andrew: They're only using it as a namespace.

[Andrew]

@SLaks: Isn't that assuming the conclusion? How do you know that's being used as a namespace without more context?

[ncubica]

well you should read this book for more professional patterns addyosmani.com/resources/essentialjsdesignpatterns/book