var $providers = {},

    $instances = {};

​

function provider(name, providerFn) {

  var providerName = name + 'Provider';

  if (typeof providerFn !== 'function') {

    return $providers[providerName];

  }

  providerFn.name = name;

  $providers[providerName] = new providerFn();

}

​

function factory(name, factoryFn) {

  provider(name, function () {

    this.$get = factoryFn;

  });

}

​

function service(name, serviceConstructor) {

  factory(name, function () {

    return new serviceConstructor();

  });

}

​

function getInstance(name) {

  if ($instances.hasOwnProperty(name)) {

    return $instances[name];

  }

  var providerInstance;

  if (undefined === (providerInstance = provider(name))) {

    throw new Error("Provider for service \"" + name + "\" not found!"); 

  }

​

  $instances[name] = providerInstance.$get();

  return $instances[name];

}

​

// примеры:

​

service('foo', function () {

  this.foo = function () {

    return 'foo';

  };

});

​

var 

   fooInstance1 = getInstance('foo'),

   fooInstance2 = getInstance('foo')

;

​

console.log(fooInstance1.foo());

console.log(fooInstance1 === fooInstance2);

​

​

​

​

​

​

​

​

​

​