What is this design called?

Question

I often see this pattern:

var suchAndSuch = new (function() {
    this.thing = "something";
    this.whoaLookAtThat = function() {
        return 4;
    }
    return {
        'thing' : thing,
        'whoaLookAtThat' : whoaLookAtThat
    }
})();

What is going on here? It's the return statement part that confuses the hell out of me.

I just don't get this particular use of an IIFE.

If nothing else, knowing what it's called would help me research it.

Answer 1

This is a combination of an immediately executing function and a (bit of a messed up) closure. I think your example maybe a bit flawed it may be better if it was:

var suchAndSuch = (function() {
    var thing = "something";
    function setThing(newThing){
        //maybe do some error checking here
        thing = newThing;
    };
    function getThing(){
        return thing;
    };

    return {
        getThing : getThing,
        setThing : setThing
    }
})();

Then you would have a function that executes immediately returning a new object that effectively gives a private variable and an accessor function. I have used constructs like these many times.

Answer 2

This is kind of an attempt to have public/private variables in JavaScript... I believe it is referred to as the modular pattern.

var suchAndSuch = (function() {
    var privateVariable = "something";
    var privateFunction = function() {
        return 4;
    }
    return {
        publicMethod1: function() {
            return privateVariable;
        },
        publicMethod2: function() {
            return privateFunction();
        }
    }
})();

Basically any variables declared inside the IIFE will be private. Then you return an object with methods. Since the object/methods were defined in the same scope as the private variables, the methods still have access to them. However, nothing else will.