librarySystem with dependencies

librarySystem.js

// librarySystem with dependencies

  (function () {
    var libraryStorage = {};

    function librarySystem(libraryName, dependencies, callback) {
      // If librarySystem is called in 'create' mode, store the library.
      if (arguments.length === 3) {

        // If the library has dependencies, fetch the dependencies first and then store the library.
        if (dependencies.length > 0) {
          var fetchedDependencies = dependencies.map(function (dependencyName) {
            return librarySystem(dependencyName);
          });
          libraryStorage[libraryName] = callback.apply(null, fetchedDependencies);

        // If the library has no dependencies, store the library without any additional steps.
        } else {
          libraryStorage[libraryName] = callback();
        }

      // If librarySystem is called in 'use' mode, return the library.
      } else if (arguments.length === 1) {
        return libraryStorage[libraryName];

      // If librarySystem is called in neither 'create' nor 'use' mode, throw an error.
      } else {
        throw new TypeError('Invalid argument(s)');
      }
    }

    window.librarySystem = librarySystem;
  })();


// Tests

  // Test Suite 1
  librarySystem('dependency', [], function() {
    return 'loaded dependency';
  });

  librarySystem('app', ['dependency'], function(dependency) {
    return 'app with ' + dependency;
  });

  librarySystem('app'); // 'app with loaded dependency'

  // Test Suite 2
  librarySystem('name', [], function() {
    return 'Gordon';
  });

  librarySystem('company', [], function() {
    return 'Watch and Code';
  });

  librarySystem('workBlurb', ['name', 'company'], function(name, company) {
    return name + ' works at ' + company;
  });

  librarySystem('workBlurb'); // 'Gordon works at Watch and Code'