Question

If I return an object from an anonymous immediately invoked function expression where does it go? For example where does foo go in this code….

(function(){ 
    var foo;
    return foo;
})();

Does this have any useful applications?

Answer 1

Returning a value from your self-executing function without assigning that return value to a result variable is just a return value that goes nowhere and thus creates no new references to the data in your function. So as soon as the function returns, the data will be garbage collected, the same as if you didn’t have the return statement. So, this:

(function(){ 
    var foo;
    return foo;
})();

is no different than returning a value from a function and not assigning the returned value to anything.

You would do this to capture the return value:

var result = (function(){ 
    var foo = "hello";
    return foo;
})();

Working demo: http://jsfiddle.net/jfriend00/t9wJL/

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As for the usefulness of returning a value. It’s useful if you assign the return value to a variable or use it as input into some other function, but accomplishes nothing if you don’t.