gistfile1.js

// new module1.js
(function() {
  console.log('module1');

  // return a function that logs it's
  // arguments when invoked
  return function(){
    console.log(arguments);
  };
})()


// new production.js
// unminified problem for readability
(function() {
  console.log('module1');

  // return a function that logs it's
  // arguments when invoked
  return function(){
    console.log(arguments);
  };
})()(function() {
  console.log('module2');
})();
// => module1
// => [function() {
//      console.log('module2');
//    }]
// => TypeError: undefined is not a function

// the first step is to invoke the first module
(function(){console.log('module1');return function(){console.log(arguments)};})()
// => module1

// then it invokes the return value
// with module2 as arguments
(function(){ console.log(arguments) })(function() {console.log('module2');});
// => [function() {
//      console.log('module2');
//    }]

// then it tries to invoke the return value.
// console.log returns undefined so:
(undefined)();
// => TypeError: undefined is not a function