var result = (function() {

    function foo() {

        return 'a';

    }

​

    return foo();

​

    // This function gets hoisted up at runtime, replacing the already existing function. So "b" gets returned.

    function foo() {

        return 'b';

    }

​

})();

​

console.log(result); // "b"

​

// Demonstration of what happens at runtime:

var result = (function() {

    var foo = function foo() {

        return 'b';

    }

​

    return foo();

})();

​

console.log(result); // "b"