completed challange 3 : https://github.com/gordonmzhu/beasts/issues/1

librarySystem.js

(function(){
  var libraryStorage = {};
  var dependenciesGathered = [];
  function librarySystem(libraryName, dependencies, callback){
    if(arguments.length > 1){
      dependencies.forEach(function(dep){
        dependenciesGathered.push(libraryStorage[dep]);        
      });
      libraryStorage[libraryName] = callback.apply(this, dependenciesGathered);
    }else{
      return libraryStorage[libraryName];
    }
  }
  window.librarySystem = librarySystem;
})();