Namespaced object initialization inside JavaScript closure

Question

I have taken this snippet from http://frugalcoder.us/post/2010/02/11/js-classes.aspx:

if (typeof My == 'undefined')
My = {};
if (typeof My.Namespace == 'undefined')
My.Namespace = {};
//begin private closure
(function(){

    //this is a private static member that is only available in this closure
    var instances = 0;

    //this is a private static method that can be used internally
    function _incrementInstances() {
        instances++;
    }

    //Define SomeClass (js uses functions as class constructors, utilized with the "new" keyword)
    this.SomeClass = function(options) {
        //if the function is called directly, return an instance of SomeClass
        if (!(this instanceof SomeClass))
            return new SomeClass(options);

        //call static method
        _doSomething();

        //handle the options initialization here
    }

    //create a public static method for SomeClass
    this.SomeClass.getInstanceCount = function() {
        return instances; //returns the private static member value
    }

    //create an instance method for SomeClass
    this.SomeClass.prototype.doSomething = function() {
        /*Do Something Here*/
    }

//end private closure then run the closure, localized to My.Namespace
}).call(My.Namespace);

Then, inside the document.ready callback, both:

$(function () {
   My.Namespace.SomeClass({});
});

and:

$(function () {
   new My.Namespace.SomeClass({});
});

Give the following error:

Uncaught ReferenceError: SomeClass is not defined

What am I missing? I guess maybe it is because the tutorial is old (2010)?

Thanks in advance!

It's good to be fairly suspicious of JavaScript (and other web technologies) code samples older than a couple yeas; things change really quickly. — Pointy
– Pointy, Commented Apr 9, 2015 at 16:39

Pointy · Accepted Answer · 2015-04-09 16:37:40Z

1

The code is simply incorrect. It could be fixed however:

this.SomeClass = function SomeClass(options) { // <--- Name the function
    //if the function is called directly, return an instance of SomeClass
    if (!(this instanceof SomeClass))
        return new SomeClass(options);

    //call static method
    _doSomething();

    //handle the options initialization here
}

By giving the function a name like that, the symbol "SomeClass" will be available inside the function as a reference (to itself).

Note that _doSomething is not defined either, and that the constructor doesn't actually call that function that counts instances.

answered Apr 9, 2015 at 16:37

Pointy

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2 Comments

tonix Over a year ago

Thank you, it works now, yeah _doSomething() should be replaced with _incrementInstances(), BTW, is the snippet I posted considered bad practice when writing a JS library and organize the code in a namespace? Or Can I go with it?

Pointy Over a year ago

@tonix it's not bad, really, but a lot has happened over the past 5 years. In particular, a lot of work has been done on the whole notion of modules for JavaScript (AMD and CommonJS and RequireJS for example).

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