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Variables or methods defined within the returning object however are available to everyone. History From a historical perspective, the Module pattern was originally developed by a number of people including Richard Cornford in It was later popularized by Douglas Crockford in his lectures. Another piece of trivia is that if you've ever played with Yahoo's YUI library, some of its features may appear quite familiar and the reason for this is that the Module pattern was a strong influence for YUI when creating their components.
Examples Let's begin looking at an implementation of the Module pattern by creating a module which is self-contained. The counter variable is actually fully shielded from our global scope so it acts just like a private variable would - its existence is limited to within the module's closure so that the only code able to access its scope are our two functions.
Our methods are effectively namespaced so in the test section of our code, we need to prefix any calls with the name of the module e. When working with the Module pattern, we may find it useful to define a simple template that we use for getting started with it. The module itself is completely self-contained in a global variable called basketModule. The basket array in the module is kept private and so other parts of our application are unable to directly read it.
It only exists with the module's closure and so the only methods able to access it are those with access to its scope i. Notice how the scoping function in the above basket module is wrapped around all of our functions, which we then call and immediately store the return value of.
This has a number of advantages including: The freedom to have private functions and private members which can only be consumed by our module. As they aren't exposed to the rest of the page only our exported API is , they're considered truly private. Given that functions are declared normally and are named, it can be easier to show call stacks in a debugger when we're attempting to discover what function s threw an exception.
J Crowder has pointed out in the past, it also enables us to return different functions depending on the environment. In the past, I've seen developers use this to perform UA testing in order to provide a code-path in their module specific to IE, but we can easily opt for feature detection these days to achieve a similar goal.
Module Pattern Variations Import mixins This variation of the pattern demonstrates how globals e. This effectively allows us to import them and locally alias them as we wish.
This takes as its first argument a dot-separated string such as myObj. Using setObject allows us to set the value of children, creating any of the intermediate objects in the rest of the path passed if they don't already exist.
For example, if we wanted to declare basket. Here, we see an example of how to define a namespace which can then be populated with a module containing both a private and public API.
Oh, and thanks to David Engfer for the joke. Disadvantages The disadvantages of the Module pattern are that as we access both public and private members differently, when we wish to change visibility, we actually have to make changes to each place the member was used. We also can't access private members in methods that are added to the object at a later point. That said, in many cases the Module pattern is still quite useful and when used correctly, certainly has the potential to improve the structure of our application.
Other disadvantages include the inability to create automated unit tests for private members and additional complexity when bugs require hot fixes.
It's simply not possible to patch privates. Instead, one must override all public methods which interact with the buggy privates.