Question

What is the difference between

var module = (function(){
    return {} 
})()

and

(function(context){
    var module = {}
    context.module = module;
})(this)

Answer 1

A property of this is not equivalent to a variable. In the global scope (i.e. where this references window), they are similiar. Yet, for example they will have a different behavior when you try to delete them:

> this.module = {};
> delete this.module
true
> var module = {};
// cant be deleted

Apart from that, both snippets create an empty object, wrapped inside a closure where you could define local (private) variables/functions etc. In your second function the object is also assigned to the local variable module, but that could be done in the first one as well.

---

@Eric: Your approach, using the new operator, is similiar to the first one regarding the variable. However, it will create an instance of that anonymous function instead of returning a plain object. It will inherit properties from a custom prototype, so for example module.constructor will then point to the anonymous function (which cannot be garbage collected, but e.g. even reused to create a clone). I would not recommend to use this.