I've been using IIFE in JavaScript and in AngularJS and have been using the following structure:

Method 1:

//IIFE Immediately Invoked Function Expression
(function () {


}());

However, I've seen the following often where a variable is assigned to the IIFE

Method 2:

//IIFE Immediately Invoked Function Expression assigned to doStuff variable
var doStuff = (function () {


}());

NOTE: This question is NOT about what this pattern is or what an IIFE is. This is pertaining specifically to why one would use a return variable on an IIFE and its relation to Angular practices as well.

In Angular Method 1 works fine, but in many of the raw JS examples I see, Method 2 is used. My assumption is that anything encasulated in doStuff will be avliable via it and callable. However, I'm not 100% sure on the exact reasoning or distinction between the 2 methods and need some help understanding when to use the different methods?

I've been using IIFE in JavaScript and in AngularJS and have been using the following structure:

Method 1:

//IIFE Immediately Invoked Function Expression
(function () {


}());

However, I've seen the following often where a variable is assigned to the IIFE

Method 2:

//IIFE Immediately Invoked Function Expression assigned to doStuff variable
var doStuff = (function () {


}());

NOTE: This question is NOT about what this pattern is or what an IIFE is. This is pertaining specifically to why one would use a return variable on an IIFE and its relation to Angular practices as well.

In Angular Method 1 works fine, but in many of the raw JS examples I see, Method 2 is used. My assumption is that anything encasulated in doStuff will be avliable via it and callable. However, I'm not 100% sure on the exact reasoning or distinction between the 2 methods and need some help understanding when to use the different methods?

• javascript
• angularjs

• @Bergi - This isn't a duplicate - please READ the question and see the difference from the link supposedly a duplicate. That link does not answer this question. – atconway Commented Oct 19, 2014 at 15:53
• 2 I'm not sure I understand the question. You seem to know what an IIFE does; now why would one use a return from an IIFE? Whenever you want a return from the expression to assign the value to doStuff; instead of just executing a void IIFE. If you're looking for use cases, you should google for "module pattern", because that's what an IIFE with a return value is called. – Bergi Commented Oct 19, 2014 at 15:59
• @Bergi - I believe the comment you just posted is actually a good explanation to what I posted and what I would call, 'an answer'. If you re-open and post that blurb as an answer I'll upvote. Don't forget, just because something is obvious to you does not mean it is to the OP (me). Also because it is obvious is not grounds for closing either. I needed specific examples and an explanation of why the return variable vs. not using. In Angular they don't have return variables all the time, yet many JS examples do use a return. I want to know and understand 'why'. – atconway Commented Oct 19, 2014 at 16:06
• 2 This is the second time I've seen the name IIFE harm understanding. If we were to call this design pattern using it's old/traditional name - "self calling function" - the reason why some are assigned to a variable and some aren't wouldn't be mysterious: because that's what functions do. Some functions return values that you use some functions don't. If people insist that self calling function is wrong then at least call it immediately invoked function expression. Just don't call it IIFE - people forget that IIFE are nothing special/magical - they're just functions. – slebetman Commented Oct 19, 2014 at 17:07
• @slebetman - I think what I was trying to get at from the Angular perspective is why we can have void return IIFEs, but yet still have publically available functions returned and available? I was looking for validation that the Angular module container where the controller being wrapped in an IIFE was the reason we could still access those functions within the IIFE that does not itself contain a return variable. However the controller itself does have a return variable and it is registered when using app.controller. – atconway Commented Oct 20, 2014 at 15:02

1 Answer 1

The reason for Method #2 is that you'll find code within the IIFE that returns something (typically, but not necessarily, an object or a function). What the IIFE returns is what ends up being assigned. E.g.:

//IIFE Immediately Invoked Function Expression assigned to doStuff variable
var doStuff = (function () {
    var privateInformationForDoStuff = 0;

    function doStuff() {
        console.log(++privateInformationForDoStuff);
    }

    return doStuff;
}());

There, the variable ends up being a reference to a function that, each time it's called, gives us a number higher than the previous time. The IIFE is there to ensure that nothing can modify the privateInformationForDoStuff variable, it's entirely private to the doStuff function.

It was common to use this (sometimes called the "revealing module pattern") to create objects with various functions on them which might also have private information that's only shared within the "module":

var MyApp = (function() {
    var privateModuleInformation;
    var morePrivateModuleInformation;
    // ...

    function doThis() {
        // ...
    }

    function doThat() {
        // ...
    }

    function doTheOther() {
        // ...
    }

    return {
        doThis: doThis,
        doThat: doThat,
        doTheOther: doTheOther
    };
})();

In modern environments you'd use an actual module instead, but that didn't used to be an option.