Beast Challenge 2 – librarySystem with dependencies

librarySystem.js

(function() {

  var libraryStorage = {};

  function librarySystem(libraryName, dependencies, callback) {
    
    if (arguments.length > 1) {
      if (dependencies.length > 0) {
        var dependenciesExistArray = dependencies.map(function(dependency) {
          return libraryStorage[dependency];
        });
      }
      
      // `.apply` allows arguments to be provided as an array to our callback
      libraryStorage[libraryName] = callback.apply(this, dependenciesExistArray);
    } else {
      return libraryStorage[libraryName];
    } 
  }

  window.librarySystem = librarySystem;

})();