Javascript: Self-invoking anonymous function example

gistfile1.js

// Immediately invoked function
// Code treated as local variables and functions
// Anonymous function, wrapped by a set of  parenthesis, allows execution of anonymous function

(function () {
  
    var foo = 'hello, window';

    var bar = function () {
        var foo = 'hello, function';
        alert(window.foo);  // returns undefined
    };

    bar();
  
}());