Your assumptions are almost correct. Let’s review those first.
- It assigns the return of a self-executing function
This is called an Immediately-invoked function expression or IIFE
- It defines a local variable within this function
This is the way of having private object fields in JavaScript as it does not provide the private keyword or functionality otherwise.
- It returns the actual function containing logic that makes use of the local variable.
Again, the main point is that this local variable is private.
Is there a name for this pattern?
AFAIK you can call this pattern Module Pattern. Quoting:
The Module pattern encapsulates “privacy”, state and organization using closures. It provides a way of wrapping a mix of public and private methods and variables, protecting pieces from leaking into the global scope and accidentally colliding with another developer’s interface. With this pattern, only a public API is returned, keeping everything else within the closure private.
Comparing those two examples, my best guesses about why the first one is used are:
- It is implementing the Singleton design pattern.
- One can control the way an object of a specific type can be created using the first example. One close match with this point can be static factory methods as described in Effective Java.
- It’s efficient if you need the same object state every time.
But if you just need the vanilla object every time, then this pattern will probably not add any value.