Simple Library Loader

librarySystem.js

// (function() {
//   var libraryStorage = {};
  
//   function librarySystem(libraryName, callback) {
//     if (arguments.length > 1) {
//       libraryStorage[libraryName] = callback();
//     } else {
//       return libraryStorage[libraryName];
//     }
//   }
  
//   window.librarySystem = librarySystem;
// })();

(function() {
  var libraryStorage = {};
  
  function librarySystem(libraryName, dependencies, callback) {
    
    if (arguments.length > 1) {
      if (dependencies.length > 0) {
        var dependenciesArray = [];        
        dependencies.forEach(function(dependency) {
          dependenciesArray.push(libraryStorage[dependency]);
        });
      }
      libraryStorage[libraryName] = callback.apply(null, dependenciesArray);
    } else {
      return libraryStorage[libraryName];
    }
  }
  
  window.librarySystem = librarySystem;
})();

librarySystem('router', [], function() {
  return {
    description: 'Supposedly, I can handle app routing.',
    dependencies: [arguments]
  };
});

librarySystem('app', ['router'], function(router) {
  return {
    description: 'Just a silly app that has a dependency',
    dependencies: [arguments]
  };
});

console.log(librarySystem('app'));