why module pattern?

I think this example could help you to clarify the usefulness of the Module Pattern.

Module Pattern

The module pattern is widely used because it provides structure and helps organize your code as it grows. Unlike other languages, JavaScript doesn’t have special syntax for packages, but the module pattern provides the tools to create self-contained decoupled pieces of code, which can be treated as black boxes of functionality and added, replaced, or removed according to the (ever-changing) requirements of the software you’re writing.

The module pattern is a combination of several patterns, namely:

Namespaces
Immediate functions
Private and privileged members
Declaring dependencies

The first step is setting up a namespace. Let’s use the namespace() function from earlier in this chapter and start an example utility module that provides useful array methods:

MYAPP.namespace('MYAPP.utilities.array');

The next step is defining the module. The pattern uses an immediate function that will provide private scope if privacy is needed. The immediate function returns an object - the actual module with its public interface, which will be available to the consumers of the module:

 MYAPP.utilities.array = (function () {
    return {
    // todo...
    };
 }());

Next, let’s add some methods to the public interface:

MYAPP.utilities.array = (function () {
   return {
      inArray: function (needle, haystack) {
         // ...
      },
      isArray: function (a) {
         // ...
      }
   };
}());

Using the private scope provided by the immediate function, you can declare some private properties and methods as needed. Right at the top of the immediate function will also be the place to declare any dependencies your module might have. Following the variable declarations, you can optionally place any one-off initialization code that helps set up the module. The final result is an object returned by the immediate function that contains the public API of your module:

MYAPP.namespace('MYAPP.utilities.array');
MYAPP.utilities.array = (function () {
   // dependencies
   var uobj = MYAPP.utilities.object,
       ulang = MYAPP.utilities.lang,
       // private properties
       array_string = "[object Array]",
       ops = Object.prototype.toString;
       // private methods
       // ...
       // end var
   // optionally one-time init procedures
   // ...
   // public API
   return {
      inArray: function (needle, haystack) {
         for (var i = 0, max = haystack.length; i < max; i += 1) {
            if (haystack[i] === needle) {
               return true;
            }
         }
      },
      isArray: function (a) {
         return ops.call(a) === array_string;
      }
      // ... more methods and properties
   };
}());

The module pattern is a widely used and highly recommended way to organize your code, especially as it grows.

Not sure why no one's answered this one properly. I can see potential for using auto-invoking functions in some kind of pattern meant to make private vars inheritable, but you're absolutely right.

There is no benefit to using the module pattern in place of a core language function constructor. It's the same exact language mechanic (closures) that allows the persistent internal vars to exist as non-accessible entities only with more code.

In JS a function constructor follows the same rules of scope as a fired function. Scope and closure is set at point of definition. The reason the internal var from a function constructor lives on is because the instance with methods defined inside the same constructor referencing that var lives on.

The only thing that changes is that you've eliminated the use of prototyped methods on the constructor and have to jury-rig your own inheritance mechanism for inherited methods.

why module pattern?

Module Pattern

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Javascript

Design Patterns

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